/* 07 — УРОК. Editorial learning session: a thread of understanding,
   a live margin, and a paper practice worksheet. Scoped to #lesson. */

#lesson {
  --ink: #14130e;
  --paper: #f2ebdb;
  --paper-deep: #e7ddc9;
  --paper-light: #fbf6eb;
  --blue: #1c3fe8;
  --blue-deep: #0f2aa8;
  --red: #f04a2f;
  --red-ink: #b82f18;
  --acid: #d8ff3e;
  --muted: #6d6759;
  --line: rgba(20, 19, 14, .18);
  position: relative;
  height: 100vh;
  min-height: 720px;
  overflow: hidden;
  isolation: isolate;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--mono);
}

#lesson ::selection { background: var(--acid); color: var(--ink); }
#lesson button, #lesson input, #lesson textarea { font: inherit; }
#lesson button { cursor: pointer; }
#lesson [hidden] { display: none !important; }

#lesson button:focus-visible,
#lesson input:focus-visible,
#lesson textarea:focus-visible,
#lesson [tabindex]:focus-visible,
#lesson a:focus-visible {
  outline: 2px solid var(--ink);
  outline-offset: 3px;
  box-shadow: 0 0 0 6px var(--acid);
}

#lesson .sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* ───────────────────────── header ───────────────────────── */

#lesson .lesson-head {
  position: absolute;
  z-index: 30;
  inset: 0 0 auto;
  height: 70px;
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr);
  align-items: center;
  gap: 18px;
  padding: 0 24px;
  background: var(--ink);
  color: var(--paper);
  border-bottom: 1px solid #2d2a23;
}

#lesson .lesson-head-left { min-width: 0; display: flex; flex-direction: column; gap: 6px; }

#lesson .lesson-brand {
  font: 800 14px/1 var(--display);
  letter-spacing: -.05em;
  white-space: nowrap;
}
#lesson .lesson-brand span { color: var(--red); }
#lesson .lesson-brand i {
  margin-left: 9px;
  font: 400 6px var(--mono);
  font-style: normal;
  letter-spacing: .15em;
  color: #837e71;
}

#lesson .lesson-breadcrumb {
  display: flex;
  align-items: center;
  gap: 7px;
  font-size: 6.5px;
  letter-spacing: .11em;
  color: #8b8577;
  white-space: nowrap;
}
#lesson .lesson-breadcrumb b { color: #575248; font-weight: 400; }
#lesson .lesson-breadcrumb strong { color: var(--acid); font-weight: 500; }

#lesson .lesson-mode-switch {
  position: relative;
  left: auto;
  top: auto;
  justify-self: center;
  display: flex;
  gap: 3px;
  padding: 3px;
  border: 1px solid #403c32;
  background: #1d1b15;
}

#lesson .lesson-mode-switch button {
  width: 132px;
  display: grid;
  grid-template-columns: 22px 1fr;
  gap: 1px 4px;
  padding: 7px 9px;
  border: 1px solid transparent;
  background: transparent;
  color: #b3ac9e;
  text-align: left;
  transition: background .2s, color .2s, border-color .2s;
}
#lesson .lesson-mode-switch button:hover { color: var(--paper); border-color: #5b5548; }
#lesson .lesson-mode-switch span { font-size: 6px; line-height: 1.4; }
#lesson .lesson-mode-switch b { font: 800 9px/1.2 var(--display); letter-spacing: -.02em; }
#lesson .lesson-mode-switch em {
  grid-column: 2;
  font-size: 6px;
  font-style: normal;
  letter-spacing: .04em;
  opacity: .62;
}
#lesson .lesson-mode-switch button.active {
  background: var(--acid);
  border-color: var(--acid);
  color: var(--ink);
}
#lesson .lesson-mode-switch button.active em { opacity: .72; }

#lesson .lesson-head-right { justify-self: end; display: flex; align-items: center; gap: 14px; }

#lesson .lesson-session {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: 6.5px;
  letter-spacing: .1em;
  color: #aaa395;
  white-space: nowrap;
}
#lesson .lesson-session > i {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--acid);
  box-shadow: 0 0 9px var(--acid);
}
#lesson .lesson-session b { font: 500 10px var(--mono); color: var(--paper); letter-spacing: .04em; }

#lesson .quiet-toggle {
  display: flex;
  align-items: center;
  min-height: 34px;
  gap: 7px;
  padding: 8px 10px;
  border: 1px solid #4d483d;
  background: transparent;
  color: #b3ac9e;
  transition: background .2s, color .2s, border-color .2s;
}
#lesson .quiet-toggle span { font-size: 11px; line-height: 1; color: var(--acid); }
#lesson .quiet-toggle b { font: 500 6.5px var(--mono); letter-spacing: .12em; }
#lesson .quiet-toggle:hover { border-color: var(--paper); color: var(--paper); }
#lesson .quiet-toggle[aria-pressed="true"] { background: var(--blue); border-color: var(--blue); color: #fff; }

/* ───────────────────────── chapter spine ───────────────────────── */

#lesson .chapter-spine {
  position: absolute;
  z-index: 12;
  left: 0;
  top: 70px;
  bottom: 0;
  width: 208px;
  display: flex;
  flex-direction: column;
  padding: 25px 18px 18px;
  border-right: 1px solid var(--ink);
  background:
    linear-gradient(135deg, rgba(20, 19, 14, .035) 25%, transparent 25%) 0 0 / 7px 7px,
    var(--paper-deep);
}

#lesson .spine-label {
  display: block;
  margin: 0;
  font: 500 6.5px var(--mono);
  letter-spacing: .17em;
  color: var(--muted);
}
#lesson .spine-head h2 {
  margin: 12px 0 8px;
  font: 800 18px/1.02 var(--display);
  letter-spacing: -.06em;
}
#lesson .spine-head h2 em { font-style: normal; color: var(--blue); }
#lesson .spine-head p { margin: 0; font-size: 6.5px; letter-spacing: .04em; color: var(--muted); }

#lesson .course-map {
  list-style: none;
  margin: 26px 0 0;
  padding: 0;
  border-top: 1px solid #b9ae96;
}
#lesson .course-map li {
  display: grid;
  grid-template-columns: 23px minmax(0, 1fr) 12px;
  gap: 7px;
  align-items: center;
  padding: 8px 5px;
  border-bottom: 1px solid #c8bda4;
  font-size: 6.5px;
  line-height: 1.35;
  color: #7a7465;
}
#lesson .course-map li span, #lesson .course-map li em {
  font: 500 6.5px var(--mono);
  font-style: normal;
  color: #8d8675;
}
#lesson .course-map li b { font-weight: 500; }
#lesson .course-map li.done { color: #5d584c; }
#lesson .course-map li.done span, #lesson .course-map li.done em { color: var(--blue); }
#lesson .course-map li.current {
  margin: 0 -5px;
  padding: 9px 10px;
  background: var(--ink);
  color: var(--paper);
}
#lesson .course-map li.current b { font-weight: 600; }
#lesson .course-map li.current span, #lesson .course-map li.current em { color: var(--acid); }

#lesson .spine-outline {
  display: flex;
  flex-direction: column;
  margin-top: 22px;
}
#lesson .spine-outline > span {
  margin-bottom: 7px;
  font: 500 6px var(--mono);
  letter-spacing: .17em;
  color: var(--muted);
}
#lesson .spine-outline button {
  display: grid;
  grid-template-columns: 19px minmax(0, 1fr) auto;
  gap: 6px;
  align-items: baseline;
  padding: 8px 0;
  border: 0;
  border-bottom: 1px solid #bcb198;
  background: transparent;
  color: #625d50;
  text-align: left;
  transition: color .18s, padding .18s;
}
#lesson .spine-outline button:hover { color: var(--ink); padding-left: 4px; }
#lesson .spine-outline button i { font: 500 6px var(--mono); font-style: normal; color: #948d7b; }
#lesson .spine-outline button b { font: 500 7px/1.35 var(--mono); }
#lesson .spine-outline button em { font: 400 5.5px var(--mono); font-style: normal; color: #958e7c; }
#lesson .spine-outline button.is-active { color: var(--blue); }
#lesson .spine-outline button.is-active i {
  display: grid;
  place-items: center;
  width: 16px;
  height: 16px;
  border-radius: 50%;
  background: var(--blue);
  color: #fff;
}
#lesson .spine-outline button.is-active em { color: var(--blue); }

#lesson .chapter-meter {
  margin-top: auto;
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: center;
  gap: 6px;
  padding-top: 15px;
  border-top: 1px solid #b9ae96;
  font-size: 6px;
  letter-spacing: .13em;
}
#lesson .chapter-meter b { grid-column: 1 / -1; height: 3px; background: #c9bea7; overflow: hidden; }
#lesson .chapter-meter b i { display: block; width: 0; height: 100%; background: var(--red); transition: width .18s; }
#lesson .chapter-meter em { font-style: normal; color: var(--ink); }

/* ───────────────────────── views ───────────────────────── */

#lesson .lesson-view {
  position: absolute;
  inset: 70px 0 0 208px;
  display: none;
}
#lesson .lesson-view.active { display: grid; }

#lesson .read-view { grid-template-columns: minmax(0, 1fr) 290px; }

/* ───────────────────────── the thread ───────────────────────── */

#lesson .lesson-thread {
  position: absolute;
  z-index: 18;
  left: max(7px, calc((100% - 290px - 930px) / 2 + 8px));
  top: 16px;
  bottom: 16px;
  width: 24px;
  pointer-events: none;
}
#lesson .thread-svg { position: absolute; inset: 0; width: 24px; height: 100%; overflow: visible; }
#lesson .thread-track {
  fill: none;
  stroke: var(--red);
  stroke-width: 2;
  opacity: .62;
  stroke-linecap: round;
}
#lesson .thread-knots span {
  position: absolute;
  left: 11px;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--paper);
  border: 2px solid var(--ink);
  box-shadow: 0 0 0 2px var(--acid);
  transform: translate(-50%, -50%);
  animation: lessonKnotIn .35s cubic-bezier(.2, .9, .2, 1.4) both;
}
#lesson .thread-bead {
  position: absolute;
  left: 11px;
  top: 0;
  width: 13px;
  height: 13px;
  border-radius: 50%;
  background: var(--blue);
  border: 2px solid var(--paper);
  box-shadow: 0 0 0 1px var(--ink), 0 0 0 4px rgba(216, 255, 62, .5);
  transform: translate(-50%, -50%);
  transition: top .16s linear;
}
#lesson .thread-percent {
  position: absolute;
  left: 23px;
  top: 0;
  transform: translateY(-50%);
  padding: 2px 4px;
  border: 1px solid var(--ink);
  background: var(--acid);
  color: var(--ink);
  font: 500 6.5px var(--mono);
  white-space: nowrap;
  transition: top .16s linear;
}
#lesson.is-read .thread-bead { background: var(--acid); }
#lesson.is-read .thread-percent::after { content: " ✓"; }
#lesson.practice-mode .lesson-thread { display: none; }

@keyframes lessonKnotIn {
  from { transform: translate(-50%, -50%) scale(0); }
  to { transform: translate(-50%, -50%) scale(1); }
}

/* ───────────────────────── reader ───────────────────────── */

#lesson .theory-reader {
  position: relative;
  height: 100%;
  min-height: 0;
  overflow-y: auto;
  overscroll-behavior: contain;
  background: var(--paper);
  scrollbar-width: thin;
  scrollbar-color: #8f8674 transparent;
  scroll-behavior: smooth;
}
#lesson .theory-reader::-webkit-scrollbar { width: 7px; }
#lesson .theory-reader::-webkit-scrollbar-thumb { background: #8f8674; border: 2px solid var(--paper); border-radius: 7px; }

#lesson .reader-progress {
  position: sticky;
  z-index: 20;
  top: 0;
  height: 3px;
  background: #d3c7b1;
}
#lesson .reader-progress i {
  display: block;
  position: relative;
  width: 0;
  height: 100%;
  background: var(--red);
  transition: width .1s linear;
}
#lesson .reader-progress i::after {
  content: "";
  position: absolute;
  right: -4px;
  top: 50%;
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--red);
  transform: translateY(-50%);
  box-shadow: 0 0 0 2px var(--paper);
}

#lesson .reader-page {
  position: relative;
  max-width: 930px;
  margin: 0 auto;
  padding: 62px clamp(46px, 6.2vw, 88px) 100px;
  background-color: var(--paper);
  background-image:
    linear-gradient(90deg, transparent 0 52px, rgba(240, 74, 47, .18) 52px 53px, transparent 53px),
    repeating-linear-gradient(0deg, transparent 0 31px, rgba(20, 19, 14, .045) 31px 32px);
  background-size: auto, 100% 32px;
  overflow: hidden;
}

#lesson .chapter-ghost {
  position: absolute;
  z-index: 0;
  right: -12px;
  top: 14px;
  font: 900 clamp(170px, 21vw, 310px)/.8 var(--display);
  letter-spacing: -.13em;
  color: #e5dbc7;
  user-select: none;
  pointer-events: none;
}

#lesson .reader-kicker {
  position: relative;
  z-index: 2;
  display: flex;
  align-items: center;
  gap: 9px;
  font: 500 6.5px var(--mono);
  letter-spacing: .16em;
  color: var(--red-ink);
  margin-bottom: 18px;
}
#lesson .reader-kicker i { width: 18px; height: 1px; background: #b9ad96; }
#lesson .reader-kicker span:nth-of-type(n+2) { color: var(--muted); }
#lesson .reader-kicker b {
  margin-left: auto;
  font: 400 6px var(--mono);
  letter-spacing: .06em;
  color: var(--muted);
}

#lesson .reader-page > h1 {
  position: relative;
  z-index: 2;
  margin: 0;
  max-width: 10ch;
  font: 900 clamp(46px, 5.25vw, 75px)/.855 var(--display);
  letter-spacing: -.09em;
}
#lesson .reader-page > h1 em {
  font-style: normal;
  color: var(--blue);
  -webkit-text-stroke: 1.5px var(--ink);
  text-shadow: 4px 5px 0 var(--ink);
}

#lesson .reader-lead {
  position: relative;
  z-index: 2;
  max-width: 640px;
  margin: 34px 0 30px;
  padding-left: 22px;
  border-left: 3px solid var(--red);
  font: 500 clamp(17px, 1.45vw, 21px)/1.55 var(--sans);
  letter-spacing: -.015em;
}

#lesson .markable {
  cursor: pointer;
  transition: background-color .2s, color .2s;
}
#lesson .markable:hover { background: rgba(255, 239, 138, .62); }
#lesson .markable.highlighted {
  background: linear-gradient(transparent 12%, var(--acid) 12% 92%, transparent 92%);
  box-decoration-break: clone;
  -webkit-box-decoration-break: clone;
}
#lesson .markable { position: relative; }
#lesson .markable.highlighted::before {
  content: "✓";
  position: absolute;
  left: -25px;
  top: .18em;
  width: 15px;
  height: 15px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--blue);
  color: #fff;
  font: 700 8px var(--mono);
}

#lesson .reader-sidehint { display: none; }

#lesson .theory-rule {
  position: relative;
  z-index: 2;
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 14px;
  align-items: center;
  margin: 18px 0 38px;
}
#lesson .theory-rule span { font: 800 12px var(--display); letter-spacing: -.04em; }
#lesson .theory-rule i { position: relative; height: 1px; background: var(--ink); }
#lesson .theory-rule i::after {
  content: "→";
  position: absolute;
  right: 0;
  top: -9px;
  font: 500 10px var(--mono);
}
#lesson .theory-rule b {
  font: 500 6.5px/1.45 var(--mono);
  text-align: right;
  letter-spacing: .04em;
  color: var(--muted);
}

/* mobile-only in-page table of contents */
#lesson .reader-toc { display: none; }

/* ───────────────────────── theory sections ───────────────────────── */

#lesson [id^="theory-"] { scroll-margin-top: 16px; }

#lesson .markable.is-flash {
  animation: lessonFlash .8s ease;
}
@keyframes lessonFlash {
  0%, 100% { box-shadow: 0 0 0 0 rgba(28, 63, 232, 0); }
  35% { box-shadow: 0 0 0 5px rgba(28, 63, 232, .26); }
}

#lesson .theory-section {
  position: relative;
  display: grid;
  grid-template-columns: 42px minmax(0, 1fr);
  gap: 24px;
  margin: 64px 0;
}
#lesson .section-index {
  width: 34px;
  height: 34px;
  display: grid;
  place-items: center;
  border: 1px solid var(--ink);
  border-radius: 50%;
  font: 500 7px var(--mono);
}
#lesson .theory-section-body { min-width: 0; }
#lesson .theory-section h2 {
  max-width: 22ch;
  margin: 2px 0 20px;
  font: 800 clamp(23px, 2.4vw, 31px)/1.02 var(--display);
  letter-spacing: -.06em;
}
#lesson .theory-section p {
  max-width: 63ch;
  margin: 0 0 15px;
  font: 400 16px/1.72 var(--sans);
  letter-spacing: -.006em;
  color: #27251e;
}
#lesson .theory-section p b { font-weight: 700; }
#lesson .theory-section p .markable { display: inline; }

/* figure */
#lesson .riemann-figure {
  margin: 30px 0 0;
  padding: 15px 17px 13px;
  background: #171610;
  color: var(--paper);
  border: 1px solid #000;
  box-shadow: 6px 6px 0 var(--blue);
}
#lesson .figure-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  font: 500 6px var(--mono);
  letter-spacing: .14em;
  color: #aba597;
}
#lesson .figure-head b { color: var(--acid); font: 500 7px var(--mono); letter-spacing: .04em; }
#lesson .riemann-figure svg { display: block; width: 100%; height: auto; margin: 10px 0 6px; overflow: visible; }
#lesson .riemann-figure .area { fill: url(#curveFill); opacity: .58; }
#lesson .riemann-figure .curve, #lesson .riemann-figure .axis { fill: none; stroke: #f7f0e0; stroke-width: 2; }
#lesson .riemann-figure .rects rect {
  fill: rgba(28, 63, 232, .44);
  stroke: #f7f0e0;
  stroke-width: 1;
  transition: fill .18s;
}
#lesson .riemann-figure:hover .rects rect { fill: rgba(28, 63, 232, .58); }
#lesson .figure-control {
  display: grid;
  grid-template-columns: 1fr 120px auto;
  align-items: center;
  gap: 12px;
  padding-top: 5px;
  border-top: 1px solid #3b382e;
  font: 400 6px var(--mono);
  letter-spacing: .12em;
  color: #999385;
}
#lesson .figure-control label span { color: var(--acid); }
#lesson .figure-control input {
  width: 100%;
  height: 14px;
  accent-color: var(--acid);
  cursor: ew-resize;
}
#lesson .figure-tip { color: #777264; }
#lesson .riemann-figure figcaption {
  display: flex;
  gap: 12px;
  margin-top: 7px;
  font: 400 6.5px/1.5 var(--mono);
  color: #b8b2a4;
}
#lesson .riemann-figure figcaption span { color: var(--acid); }

/* pull quote */
#lesson .reader-page blockquote {
  position: relative;
  margin: 72px -14px;
  padding: 40px 7% 38px;
  display: grid;
  grid-template-columns: 48px minmax(0, 1fr);
  background: var(--blue);
  color: #fff;
  border: 1px solid var(--ink);
  box-shadow: 9px 9px 0 var(--ink);
  transform: rotate(-.6deg);
}
#lesson .reader-page blockquote > span {
  font: 900 72px/.72 var(--serif);
  color: var(--acid);
}
#lesson .reader-page blockquote p {
  margin: 0;
  font: 800 clamp(24px, 3vw, 38px)/1.1 var(--display);
  letter-spacing: -.065em;
}
#lesson .reader-page blockquote p b { color: var(--acid); }

/* formula */
#lesson .formula-section { grid-template-columns: 42px minmax(0, 1fr); }
#lesson .hero-formula {
  position: relative;
  margin-top: 24px;
  padding: 25px 27px 22px;
  background: var(--paper-light);
  border: 2px solid var(--ink);
  box-shadow: 9px 9px 0 var(--red);
  display: flex;
  flex-direction: column;
}
#lesson .hero-formula small { font: 500 6.5px var(--mono); letter-spacing: .15em; color: var(--muted); }
#lesson .hero-formula > b {
  margin: 16px 0 15px;
  font: 700 clamp(20px, 2.8vw, 36px)/1.15 var(--serif);
  letter-spacing: -.02em;
  overflow-wrap: anywhere;
}
#lesson .hero-formula sub, #lesson .hero-formula sup { font-size: .5em; }
#lesson .formula-steps {
  display: flex;
  flex-wrap: wrap;
  gap: 7px;
  align-items: center;
  padding-top: 12px;
  border-top: 1px solid var(--line);
  font: 500 6.5px var(--mono);
  letter-spacing: .06em;
  color: #4d483d;
}
#lesson .formula-steps span { padding: 4px 6px; background: #e8dfcc; }
#lesson .formula-steps i { font-style: normal; color: var(--red-ink); }
#lesson .hero-formula em {
  margin-top: 12px;
  font: 400 6.5px var(--mono);
  font-style: normal;
  color: #797266;
}

/* example */
#lesson .example-block {
  position: relative;
  margin: 72px 0 58px;
  padding: 25px 30px 27px;
  background: var(--acid);
  border: 2px solid var(--ink);
  box-shadow: 10px 10px 0 var(--ink);
}
#lesson .example-block > div {
  display: flex;
  justify-content: space-between;
  font: 500 6.5px var(--mono);
  letter-spacing: .15em;
}
#lesson .example-block h3 {
  max-width: 31ch;
  margin: 13px 0 20px;
  font: 800 clamp(22px, 2.4vw, 29px)/1.12 var(--display);
  letter-spacing: -.06em;
}
#lesson .example-block h3 i { font: 700 1.02em var(--serif); font-style: italic; letter-spacing: -.02em; }
#lesson .example-block ol {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 16px;
  margin: 0;
  padding: 0;
  list-style: none;
}
#lesson .example-block li { padding-top: 10px; border-top: 1px solid var(--ink); }
#lesson .example-block li span { font: 500 6.5px var(--mono); }
#lesson .example-block li p { margin: 6px 0 0; font: 400 12px/1.55 var(--mono); }
#lesson .example-block li strong { font: 800 29px var(--display); color: var(--red); }

/* checkpoint */
#lesson .reader-checkpoint {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 24px;
  align-items: center;
  margin: 0 0 66px;
  padding: 24px 27px;
  background: var(--ink);
  color: var(--paper);
  border-left: 5px solid var(--red);
}
#lesson .reader-checkpoint span { font: 500 6px var(--mono); letter-spacing: .16em; color: var(--acid); }
#lesson .reader-checkpoint h3 {
  max-width: 31ch;
  margin: 8px 0 0;
  font: 700 clamp(18px, 2vw, 24px)/1.15 var(--display);
  letter-spacing: -.05em;
}
#lesson .reader-checkpoint button {
  padding: 11px 13px;
  border: 1px solid var(--acid);
  background: transparent;
  color: var(--acid);
  font: 600 7px var(--mono);
  letter-spacing: .08em;
  white-space: nowrap;
  transition: background .2s, color .2s;
}
#lesson .reader-checkpoint button b { margin-left: 12px; }
#lesson .reader-checkpoint button:hover { background: var(--acid); color: var(--ink); }

/* finish */
#lesson .reader-finish {
  margin: 0 -14px;
  padding: 54px 20px 8px;
  border-top: 1px solid var(--ink);
  text-align: center;
}
#lesson .reader-finish > span { font: 500 6px var(--mono); letter-spacing: .19em; color: var(--red-ink); }
#lesson .reader-finish h2 {
  margin: 14px 0 18px;
  font: 900 clamp(31px, 4.6vw, 56px)/.92 var(--display);
  letter-spacing: -.085em;
}
#lesson .reader-finish h2 em { font-style: normal; color: var(--red); }
#lesson .finish-meta {
  display: flex;
  justify-content: center;
  gap: 9px;
  align-items: center;
  margin-bottom: 22px;
  font: 500 6.5px var(--mono);
  letter-spacing: .06em;
  color: var(--muted);
}
#lesson .finish-meta i { width: 14px; height: 1px; background: #b9ad96; }
#lesson .reader-finish button {
  padding: 15px 19px;
  border: 2px solid var(--ink);
  background: var(--ink);
  color: var(--paper);
  font: 700 8px var(--mono);
  letter-spacing: .1em;
  transition: transform .2s, box-shadow .2s;
}
#lesson .reader-finish button:hover { transform: translate(-2px, -2px); box-shadow: 5px 5px 0 var(--red); }
#lesson .reader-finish button b { margin-left: 28px; color: var(--acid); }

/* ───────────────────────── margin / notes ───────────────────────── */

#lesson .reader-margin {
  position: relative;
  height: 100%;
  min-height: 0;
  display: flex;
  flex-direction: column;
  padding: 21px 18px 17px;
  background:
    linear-gradient(90deg, rgba(255, 255, 255, .055) 1px, transparent 1px) 0 0 / 22px 22px,
    linear-gradient(0deg, rgba(255, 255, 255, .055) 1px, transparent 1px) 0 0 / 22px 22px,
    var(--blue);
  color: #fff;
  border-left: 1px solid var(--ink);
  overflow: hidden;
}

#lesson .margin-head { display: flex; align-items: flex-start; justify-content: space-between; gap: 10px; }
#lesson .margin-head > div:first-child > span {
  display: block;
  font: 500 6px var(--mono);
  letter-spacing: .16em;
  color: #b9c4ff;
}
#lesson .margin-head > div:first-child > b {
  display: block;
  margin-top: 7px;
  font: 700 10px/1.25 var(--mono);
  letter-spacing: -.01em;
}
#lesson .margin-head-actions { display: flex; gap: 6px; }
#lesson .margin-head-actions button {
  width: 29px;
  height: 29px;
  display: grid;
  place-items: center;
  padding: 0;
  border: 1px solid rgba(255, 255, 255, .7);
  background: transparent;
  color: #fff;
  font: 400 16px/1 var(--mono);
  transition: background .2s, color .2s;
}
#lesson .margin-head-actions button:hover { background: var(--acid); border-color: var(--acid); color: var(--ink); }
#lesson #notesClose { display: none; }

#lesson .margin-hint {
  margin: 13px 0 15px;
  padding-left: 9px;
  border-left: 1px solid rgba(255, 255, 255, .45);
  font: 400 6px/1.5 var(--mono);
  letter-spacing: .03em;
  color: #c5ceff;
}

#lesson .note-composer {
  margin: 0 0 13px;
  padding: 12px;
  background: var(--paper-light);
  color: var(--ink);
  border: 1px solid var(--ink);
  box-shadow: 4px 4px 0 #0b1f91;
}
#lesson .composer-label { display: block; font: 500 6px var(--mono); letter-spacing: .16em; color: var(--red-ink); }
#lesson .note-composer blockquote {
  margin: 7px 0;
  padding-left: 7px;
  border-left: 2px solid var(--red);
  font: 500 13px/1.3 var(--hand);
  color: #544d3f;
}
#lesson .note-composer textarea {
  width: 100%;
  min-height: 57px;
  margin-top: 7px;
  padding: 7px 4px;
  border: 0;
  border-bottom: 1px solid var(--ink);
  outline: 0;
  resize: vertical;
  background: repeating-linear-gradient(transparent 0 23px, rgba(20, 19, 14, .12) 23px 24px);
  color: var(--ink);
  font: 600 15px/24px var(--hand);
}
#lesson .note-composer textarea::placeholder { color: #9e9583; }
#lesson .composer-actions { display: flex; gap: 6px; margin-top: 8px; }
#lesson .composer-actions button {
  padding: 7px 8px;
  border: 1px solid var(--ink);
  background: var(--ink);
  color: var(--paper);
  font: 600 6px var(--mono);
  letter-spacing: .08em;
}
#lesson .composer-actions button + button { background: transparent; color: var(--ink); }
#lesson .composer-actions button:hover { background: var(--blue); border-color: var(--blue); color: #fff; }

#lesson .note-status {
  min-height: 0;
  margin: 0;
  font: 500 6px var(--mono);
  letter-spacing: .08em;
  color: var(--acid);
  opacity: 0;
  transition: opacity .2s;
}
#lesson .note-status.show { min-height: 12px; opacity: 1; }

#lesson .note-stack {
  display: flex;
  flex-direction: column;
  gap: 11px;
  min-height: 0;
  flex: 0 1 auto;
  overflow-y: auto;
  padding: 2px 3px 7px 1px;
  scrollbar-width: thin;
  scrollbar-color: rgba(255, 255, 255, .5) transparent;
}
#lesson .note-stack::-webkit-scrollbar { width: 4px; }
#lesson .note-stack::-webkit-scrollbar-thumb { background: rgba(255, 255, 255, .45); }

#lesson .margin-note {
  position: relative;
  margin: 0;
  padding: 14px 13px 13px 20px;
  background: var(--paper-light);
  color: var(--ink);
  border: 1px solid var(--ink);
  box-shadow: 4px 5px 0 #0b1f91;
  transform: rotate(-.55deg);
}
#lesson .margin-note:nth-child(even) { transform: rotate(.45deg); background: var(--acid); }
#lesson .margin-note > i {
  position: absolute;
  left: 8px;
  top: 11px;
  bottom: 11px;
  width: 2px;
  background: var(--red);
}
#lesson .margin-note > span { display: block; font: 500 6px var(--mono); letter-spacing: .14em; color: var(--red-ink); }
#lesson .margin-note:nth-child(even) > span { color: #3d3a14; }
#lesson .margin-note p { margin: 7px 0 0; font: 600 14px/1.26 var(--hand); }
#lesson .margin-note blockquote {
  margin: 6px 0 4px;
  padding-left: 6px;
  border-left: 1px solid var(--ink);
  font: 500 12px/1.25 var(--hand);
  color: #5a5345;
}
#lesson .margin-note.user-note > span { color: var(--blue); }
#lesson .margin-note .note-delete {
  position: absolute;
  top: 5px;
  right: 5px;
  width: 18px;
  height: 18px;
  border: 0;
  background: transparent;
  color: #6b6355;
  font: 400 12px/1 var(--mono);
}
#lesson .margin-note .note-delete:hover { background: var(--ink); color: var(--paper); }

#lesson .thought-board {
  display: flex;
  flex: 1 1 auto;
  flex-direction: column;
  margin-top: 13px;
  padding-top: 11px;
  border-top: 1px solid rgba(255, 255, 255, .5);
  min-height: 72px;
  overflow: hidden;
}
#lesson .thought-board-head { display: flex; justify-content: space-between; gap: 8px; align-items: baseline; flex: 0 0 auto; }
#lesson .thought-board-head span { font: 500 6px var(--mono); letter-spacing: .15em; }
#lesson .thought-board-head b { font: 400 6px var(--mono); color: #c5ceff; font-weight: 400; }
#lesson .thought-list {
  display: flex;
  flex-direction: column;
  min-height: 0;
  overflow-y: auto;
  scrollbar-width: thin;
  scrollbar-color: rgba(255, 255, 255, .4) transparent;
}
#lesson .thought-empty {
  display: flex;
  flex: 1;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 9px;
  min-height: 58px;
  margin-top: 8px;
  padding: 18px 12px;
  border: 1px dashed rgba(255, 255, 255, .3);
  color: #d6ddff;
  text-align: center;
}
#lesson .empty-quote-mark {
  font: 900 66px/.52 var(--serif);
  color: var(--acid);
  opacity: .92;
}
#lesson .empty-quote {
  margin: 5px 0 0;
  font: 600 23px/1.05 var(--hand);
  color: #fff;
}
#lesson .thought-empty em {
  margin-top: 5px;
  font: 400 6.5px/1.55 var(--mono);
  font-style: normal;
  letter-spacing: .03em;
  color: #c5ceff;
}
#lesson .thought-list button {
  display: grid;
  grid-template-columns: 22px minmax(0, 1fr);
  gap: 7px;
  align-items: baseline;
  width: 100%;
  padding: 7px 0;
  border: 0;
  border-bottom: 1px solid rgba(255, 255, 255, .17);
  background: transparent;
  color: #fff;
  text-align: left;
}
#lesson .thought-list button:hover b { color: var(--acid); }
#lesson .thought-list button i {
  display: grid;
  place-items: center;
  width: 18px;
  height: 18px;
  border: 1px solid var(--acid);
  border-radius: 50%;
  color: var(--acid);
  font: 500 6px var(--mono);
  font-style: normal;
}
#lesson .thought-list button b {
  min-width: 0;
  font: 400 7px/1.45 var(--mono);
  font-weight: 400;
  overflow: hidden;
  display: -webkit-box;
  -webkit-line-clamp: 2;
  -webkit-box-orient: vertical;
}

#lesson .highlight-counter {
  margin-top: auto;
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 9px;
  align-items: center;
  padding-top: 12px;
  border-top: 1px solid rgba(255, 255, 255, .5);
}
#lesson .highlight-counter b { font: 800 34px/.85 var(--display); letter-spacing: -.06em; }
#lesson .highlight-counter span { font: 400 6.5px/1.3 var(--mono); }
#lesson .highlight-counter em {
  grid-column: 2;
  font: 400 6px var(--mono);
  font-style: normal;
  color: var(--acid);
}

#lesson .focus-reading {
  display: flex;
  align-items: center;
  min-height: 36px;
  gap: 8px;
  width: 100%;
  margin-top: 12px;
  padding: 9px 10px;
  border: 1px solid rgba(255, 255, 255, .6);
  background: rgba(255, 255, 255, .06);
  color: #fff;
  font: 500 6.5px var(--mono);
  letter-spacing: .09em;
  transition: background .2s, color .2s;
}
#lesson .focus-reading i { font-style: normal; color: var(--acid); }
#lesson .focus-reading span { flex: 1; text-align: left; }
#lesson .focus-reading kbd {
  padding: 2px 4px;
  border: 1px solid rgba(255, 255, 255, .5);
  font: 400 5.5px var(--mono);
  letter-spacing: .04em;
}
#lesson .focus-reading:hover { background: var(--acid); border-color: var(--acid); color: var(--ink); }
#lesson .focus-reading:hover i { color: var(--ink); }
#lesson .focus-reading:hover kbd { border-color: var(--ink); }

/* mobile notes trigger / backdrop */
  #lesson .notes-fab {
  display: none;
  position: fixed;
  z-index: 42;
  right: 20px;
  bottom: 22px;
  min-height: 42px;
  align-items: center;
  gap: 9px;
  padding: 10px 12px;
  border: 1px solid var(--ink);
  background: var(--ink);
  color: var(--paper);
  box-shadow: 4px 4px 0 var(--blue);
  font: 600 6.5px var(--mono);
  letter-spacing: .12em;
}
#lesson .notes-fab b {
  display: grid;
  place-items: center;
  width: 19px;
  height: 19px;
  border-radius: 50%;
  background: var(--acid);
  color: var(--ink);
  font: 700 7px var(--mono);
}
#lesson .notes-fab:hover { transform: translate(-1px, -1px); box-shadow: 6px 6px 0 var(--blue); }
#lesson .notes-fab.is-pulsing { animation: lessonPulse .45s ease; }

#lesson.is-selecting .notes-fab,
#lesson.is-selecting .quiet-exit.is-visible {
  opacity: 0;
  pointer-events: none;
}
@keyframes lessonPulse {
  50% { transform: scale(1.06); box-shadow: 7px 7px 0 var(--acid); }
}
#lesson .notes-backdrop { display: none; }

#lesson .quiet-exit { display: none; }

/* ───────────────────────── selection toolbar ───────────────────────── */

#lesson .selection-tool {
  position: fixed;
  z-index: 70;
  display: flex;
  align-items: center;
  gap: 4px;
  max-width: min(450px, calc(100vw - 24px));
  padding: 5px;
  background: var(--ink);
  color: var(--paper);
  border: 1px solid #413d32;
  box-shadow: 5px 5px 0 var(--blue);
}
#lesson .selection-tool > span {
  max-width: 190px;
  padding: 0 6px;
  overflow: hidden;
  white-space: nowrap;
  text-overflow: ellipsis;
  font: 400 7px var(--mono);
  color: #bdb6a8;
}
#lesson .selection-tool button {
  padding: 7px 8px;
  border: 1px solid #5d574a;
  background: transparent;
  color: var(--acid);
  font: 600 6px var(--mono);
  letter-spacing: .06em;
  white-space: nowrap;
}
#lesson .selection-tool button:hover { background: var(--acid); color: var(--ink); border-color: var(--acid); }
#lesson #selectionDismiss { color: #aaa395; }

/* ───────────────────────── practice ───────────────────────── */

#lesson .practice-view {
  grid-template-columns: 190px minmax(0, 1fr) 280px;
  background:
    radial-gradient(circle at 82% 8%, #3d5dff 0, transparent 26%),
    var(--blue);
  color: #fff;
  overflow: hidden;
}

#lesson .practice-topline {
  position: absolute;
  z-index: 8;
  inset: 0 0 auto;
  height: 48px;
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 0 16px;
  background: var(--ink);
  border-bottom: 1px solid #343027;
  font: 500 6.5px var(--mono);
  letter-spacing: .1em;
}
#lesson .back-to-theory {
  padding: 6px 8px;
  border: 1px solid #5d574a;
  background: transparent;
  color: #c5bdae;
  font: 500 6.5px var(--mono);
  letter-spacing: .08em;
  white-space: nowrap;
}
#lesson .back-to-theory:hover { border-color: var(--acid); color: var(--acid); }
#lesson .practice-steps { margin: auto; display: flex; align-items: center; gap: 6px; }
#lesson .practice-steps i {
  width: 9px;
  height: 9px;
  border: 1px solid #938c7d;
  border-radius: 50%;
  transition: background .25s, border-color .25s;
}
#lesson .practice-steps i.done { background: var(--acid); border-color: var(--acid); }
#lesson .practice-steps b { margin-left: 7px; color: var(--paper); font: 600 8px var(--mono); }
#lesson .practice-steps.score-bump { animation: lessonPulse .4s ease; }
#lesson .practice-topline-end { display: flex; align-items: center; gap: 12px; color: #9b9485; }
#lesson .practice-topline-end em { font-style: normal; color: var(--acid); letter-spacing: .06em; }

/* index */
#lesson .problem-index {
  display: flex;
  flex-direction: column;
  min-height: 0;
  padding: 67px 15px 18px;
  background: #12110d;
  border-right: 1px solid #ffffff24;
  overflow-y: auto;
}
#lesson .problem-index > span { font: 500 6px var(--mono); letter-spacing: .16em; color: #8f8879; margin-bottom: 20px; }
#lesson .problem-path { position: relative; display: flex; flex-direction: column; }
#lesson .problem-path::before {
  content: "";
  position: absolute;
  left: 12px;
  top: 18px;
  bottom: 18px;
  width: 1px;
  background: #49443a;
}
#lesson .problem-path button {
  position: relative;
  display: grid;
  grid-template-columns: 27px minmax(0, 1fr) 14px;
  gap: 7px;
  align-items: center;
  padding: 13px 3px;
  border: 0;
  border-bottom: 1px solid #302c24;
  background: transparent;
  color: #898376;
  text-align: left;
  transition: color .2s, padding .2s;
}
#lesson .problem-path button:hover { color: var(--paper); padding-left: 7px; }
#lesson .problem-path button i {
  display: grid;
  place-items: center;
  width: 24px;
  height: 24px;
  border: 1px solid #645e51;
  border-radius: 50%;
  background: #12110d;
  font: 500 6px var(--mono);
  font-style: normal;
  z-index: 1;
}
#lesson .problem-path button b { font: 500 7.5px/1.35 var(--mono); }
#lesson .problem-path button em { font: 500 7px var(--mono); font-style: normal; }
#lesson .problem-path button.active { color: var(--paper); }
#lesson .problem-path button.active i { background: var(--acid); border-color: var(--acid); color: var(--ink); }
#lesson .problem-path button.active em { color: var(--acid); }
#lesson .problem-path button.correct em { color: var(--acid); }

#lesson .attempts {
  margin-top: auto;
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: end;
  gap: 0;
  padding: 11px;
  border: 1px solid #5a5447;
  background: #ffffff08;
}
#lesson .attempts span { font: 400 5.5px var(--mono); letter-spacing: .14em; color: #a7a092; }
#lesson .attempts b { grid-row: 1 / 3; grid-column: 2; color: var(--acid); font: 800 28px/.8 var(--display); }
#lesson .attempts em { font: 400 6px var(--mono); font-style: normal; color: #a7a092; }
#lesson .index-note {
  margin: 13px 0 0;
  font: 400 6px/1.5 var(--mono);
  letter-spacing: .04em;
  color: #8f8879;
}

/* paper worksheet */
#lesson .problem-stage {
  position: relative;
  display: flex;
  flex-direction: column;
  min-height: 0;
  margin: 66px 20px 20px 0;
  padding: 36px clamp(24px, 3.2vw, 47px) 23px;
  overflow-y: auto;
  background-color: var(--paper);
  background-image: repeating-linear-gradient(0deg, transparent 0 31px, rgba(20, 19, 14, .035) 31px 32px);
  background-size: 100% 32px;
  color: var(--ink);
  border: 2px solid var(--ink);
  box-shadow: 10px 10px 0 #11100d;
  scrollbar-width: thin;
  scrollbar-color: #8f8674 transparent;
}
#lesson .problem-stage::-webkit-scrollbar { width: 6px; }
#lesson .problem-stage::-webkit-scrollbar-thumb { background: #8f8674; }
#lesson .problem-stage::before {
  content: "";
  position: absolute;
  right: -90px;
  top: 28px;
  width: 360px;
  height: 360px;
  border: 1px solid rgba(20, 19, 14, .12);
  border-radius: 50%;
  box-shadow: 0 0 0 40px rgba(20, 19, 14, .035), 0 0 0 80px rgba(20, 19, 14, .02);
  pointer-events: none;
}
#lesson .problem-meta {
  position: relative;
  z-index: 1;
  display: flex;
  justify-content: space-between;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--line);
  font: 500 6.5px var(--mono);
  letter-spacing: .15em;
  color: var(--red-ink);
}
#lesson .problem-meta b { color: var(--ink); font-weight: 500; }
#lesson .problem-stage h1 {
  position: relative;
  z-index: 1;
  margin: 22px 0 13px;
  outline: 0;
  font: 900 clamp(32px, 3.9vw, 53px)/.96 var(--display);
  letter-spacing: -.085em;
}
#lesson .problem-stage h1:focus,
#lesson .problem-stage h1:focus-visible { outline: 0; box-shadow: none; }
#lesson .problem-stage h1 em { font-style: normal; color: var(--blue); }
#lesson .problem-stage > p {
  position: relative;
  z-index: 1;
  max-width: 55ch;
  margin: 0;
  font: 400 12.5px/1.6 var(--sans);
  color: #4d473a;
}
#lesson .problem-ref {
  position: relative;
  z-index: 1;
  display: flex;
  align-items: center;
  gap: 7px;
  width: fit-content;
  max-width: 100%;
  margin: 12px 0 0;
  padding: 6px 8px;
  border: 1px solid #bdb29a;
  background: rgba(255, 255, 255, .45);
  color: #5e5749;
  font: 400 6.5px/1.4 var(--mono);
  letter-spacing: .01em;
}
#lesson .problem-ref i { width: 5px; height: 5px; flex: 0 0 auto; border-radius: 50%; background: var(--red); }

#lesson .answer-zone {
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 9px;
  margin: 19px 0 14px;
}
#lesson .choice-answer {
  min-height: 65px;
  display: grid;
  grid-template-columns: 25px minmax(0, 1fr);
  gap: 8px;
  align-items: start;
  padding: 12px 13px;
  border: 1.5px solid var(--ink);
  background: var(--paper-light);
  color: var(--ink);
  text-align: left;
  box-shadow: 2px 2px 0 transparent;
  transition: transform .16s, box-shadow .16s, background .16s, color .16s, border-color .16s;
}
#lesson .choice-answer:hover { transform: translate(-1px, -1px); box-shadow: 2px 2px 0 var(--ink); }
#lesson .choice-answer span { padding-top: 1px; font: 500 6.5px var(--mono); color: var(--red-ink); }
#lesson .choice-answer b { font: 500 10px/1.45 var(--mono); }
#lesson .choice-answer[aria-pressed="true"] { background: var(--ink); color: var(--paper); }
#lesson .choice-answer[aria-pressed="true"] span { color: var(--acid); }
#lesson .choice-answer.is-dim { opacity: .65; }
#lesson .choice-answer.is-correct { background: var(--acid); color: var(--ink); border-color: var(--ink); }
#lesson .choice-answer.is-correct span { color: var(--ink); }
#lesson .choice-answer.is-wrong { background: #ffd8ce; border-color: var(--red); color: var(--ink); }
#lesson .choice-answer.is-wrong span { color: var(--red-ink); }

#lesson .numeric-answer {
  grid-column: 1 / -1;
  width: 100%;
  padding: 5px 0 3px;
  border: 0;
  border-bottom: 3px solid var(--ink);
  outline: 0;
  background: transparent;
  color: var(--ink);
  font: 800 64px/1 var(--display);
  letter-spacing: -.06em;
}
#lesson .numeric-answer::placeholder { color: #c2b8a3; }
#lesson .numeric-answer.is-correct { border-color: var(--blue); color: var(--blue); }
#lesson .numeric-answer.is-wrong { border-color: var(--red); }

#lesson .answer-feedback {
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: 28px minmax(0, 1fr);
  gap: 8px;
  align-items: start;
  max-height: 0;
  padding: 0 12px;
  overflow: hidden;
  border: 1px solid transparent;
  background: var(--acid);
  color: var(--ink);
  transition: max-height .25s, padding .25s, margin .25s;
}
#lesson .answer-feedback.show {
  max-height: 150px;
  margin: 0 0 10px;
  padding: 10px 12px;
  border-color: var(--ink);
}
#lesson .answer-feedback span {
  display: grid;
  place-items: center;
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: var(--ink);
  color: var(--acid);
  font: 700 11px var(--mono);
}
#lesson .answer-feedback p { margin: 2px 0 0; font: 400 9px/1.55 var(--mono); }
#lesson .answer-feedback.wrong { background: #ffe2da; border-color: var(--red); }
#lesson .answer-feedback.wrong span { background: var(--red); color: #fff; }

#lesson .problem-actions {
  position: relative;
  z-index: 1;
  display: flex;
  gap: 8px;
  align-items: stretch;
  margin-top: auto;
  padding-top: 18px;
}
#lesson .problem-actions button {
  padding: 13px 15px;
  border: 1px solid var(--ink);
  background: transparent;
  color: var(--ink);
  font: 600 8px var(--mono);
  letter-spacing: .07em;
  transition: background .18s, color .18s, border-color .18s, opacity .2s;
}
#lesson .problem-actions button:hover { background: var(--ink); color: var(--paper); }
#lesson .problem-actions #hintButton span { margin-left: 4px; font-size: 5.5px; opacity: .55; }
#lesson .problem-actions #hintButton:disabled { opacity: .42; cursor: default; }
#lesson .problem-actions #hintButton:disabled:hover { background: transparent; color: var(--ink); }
#lesson .problem-actions #checkAnswer {
  min-width: 154px;
  border-color: var(--ink);
  background: var(--ink);
  color: var(--paper);
  text-align: left;
}
#lesson .problem-actions #checkAnswer b { float: right; margin-left: 24px; color: var(--acid); }
#lesson .problem-actions #checkAnswer:hover { background: var(--blue); border-color: var(--blue); }
#lesson .problem-actions .next-problem {
  margin-left: auto;
  border-color: var(--blue);
  background: var(--blue);
  color: #fff;
}
#lesson .problem-actions .next-problem span { margin-left: 13px; }
#lesson .problem-actions .next-problem:disabled {
  border-color: #bbae95;
  background: transparent;
  color: #9b917e;
  cursor: default;
}
#lesson .problem-actions .next-problem:disabled:hover { background: transparent; color: #9b917e; }
#lesson .problem-actions .next-problem:not(:disabled):hover { background: var(--blue-deep); }
#lesson .practice-keys {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin: 9px 0 0;
  font: 400 5.5px var(--mono);
  letter-spacing: .04em;
  color: var(--muted);
}
#lesson .practice-keys kbd {
  padding: 1px 3px;
  border: 1px solid #b9ae96;
  font: 400 5.5px var(--mono);
}

/* scratch */
#lesson .scratch-space {
  position: relative;
  display: flex;
  flex-direction: column;
  min-height: 0;
  padding: 65px 16px 17px;
  background:
    linear-gradient(135deg, rgba(20, 19, 14, .045) 25%, transparent 25%) 0 0 / 8px 8px,
    var(--red);
  color: var(--ink);
  border-left: 1px solid var(--ink);
  overflow-y: auto;
}
#lesson .scratch-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 8px;
  padding-bottom: 8px;
  border-bottom: 1px solid rgba(20, 19, 14, .4);
  font: 600 6.5px var(--mono);
  letter-spacing: .12em;
}
#lesson .scratch-head > div { display: flex; align-items: center; gap: 7px; }
#lesson .scratch-head button {
  padding: 3px 4px;
  border: 0;
  background: transparent;
  color: var(--ink);
  font: 500 5.5px var(--mono);
  text-decoration: underline;
  text-underline-offset: 2px;
}
#lesson #scratchToggle { display: none; }
#lesson .scratch-body { display: flex; flex-direction: column; min-height: 0; }
#lesson .scratch-space textarea {
  width: 100%;
  height: 208px;
  margin-top: 10px;
  padding: 8px 3px;
  border: 0;
  border-bottom: 1px solid rgba(20, 19, 14, .6);
  outline: 0;
  resize: none;
  background: repeating-linear-gradient(transparent 0 27px, rgba(20, 19, 14, .18) 27px 28px);
  color: var(--ink);
  font: 600 15px/28px var(--hand);
}
#lesson .scratch-space textarea::placeholder { color: rgba(101, 34, 23, .75); }
#lesson .scratch-formulas { display: flex; margin-top: 10px; border-bottom: 1px solid var(--ink); }
#lesson .scratch-formulas button {
  flex: 1;
  padding: 7px 0;
  border: 0;
  border-right: 1px solid rgba(20, 19, 14, .4);
  background: transparent;
  color: var(--ink);
  font: 700 12px var(--serif);
}
#lesson .scratch-formulas button:last-child { border-right: 0; }
#lesson .scratch-formulas button:hover { background: rgba(255, 255, 255, .22); }
#lesson .confidence { margin-top: 21px; }
#lesson .confidence > span { display: flex; justify-content: space-between; font: 500 6px var(--mono); letter-spacing: .06em; }
#lesson .confidence > span b { color: var(--paper); background: var(--ink); padding: 1px 4px; font-weight: 500; }
#lesson .confidence input { width: 100%; margin-top: 9px; accent-color: var(--ink); cursor: ew-resize; }
#lesson .confidence > div { display: flex; justify-content: space-between; margin-top: 4px; font: 400 5.5px var(--mono); }
#lesson .confidence i { font-style: normal; }
#lesson .xp-orb {
  width: 108px;
  height: 108px;
  margin: auto auto 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  border: 2px solid var(--ink);
  border-radius: 50%;
  background: var(--paper-light);
  box-shadow: 6px 7px 0 var(--ink);
  flex: 0 0 auto;
}
#lesson .xp-orb span { font: 500 5.5px var(--mono); letter-spacing: .12em; }
#lesson .xp-orb b { font: 800 26px/.95 var(--display); letter-spacing: -.06em; }
#lesson .xp-orb em { font: 500 6px var(--mono); font-style: normal; }

/* completion */
#lesson .practice-complete {
  position: absolute;
  z-index: 60;
  inset: 0;
  display: grid;
  place-items: center;
  padding: 24px;
}
#lesson .practice-complete[hidden] { display: none !important; }
#lesson .complete-backdrop { position: absolute; inset: 0; background: rgba(10, 10, 8, .74); }
#lesson .complete-card {
  position: relative;
  width: min(510px, 100%);
  padding: 34px 36px 30px;
  background: var(--paper-light);
  color: var(--ink);
  border: 2px solid var(--ink);
  box-shadow: 12px 12px 0 var(--acid);
  outline: 0;
}
#lesson .complete-close {
  position: absolute;
  top: 8px;
  right: 9px;
  width: 26px;
  height: 26px;
  border: 1px solid var(--ink);
  background: transparent;
  color: var(--ink);
  font: 400 16px/1 var(--mono);
}
#lesson .complete-close:hover { background: var(--ink); color: var(--paper); }
#lesson .complete-kicker { font: 500 6px var(--mono); letter-spacing: .18em; color: var(--red-ink); }
#lesson .complete-card h2 {
  margin: 13px 0 20px;
  font: 900 clamp(30px, 4vw, 47px)/.92 var(--display);
  letter-spacing: -.08em;
}
#lesson .complete-card h2 em { font-style: normal; color: var(--blue); }
#lesson .complete-stats {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  border-top: 1px solid var(--ink);
  border-bottom: 1px solid var(--ink);
}
#lesson .complete-stats > div { padding: 11px 8px 9px; border-right: 1px solid var(--line); }
#lesson .complete-stats > div:last-child { border-right: 0; }
#lesson .complete-stats span { display: block; font: 500 5.5px var(--mono); letter-spacing: .14em; color: var(--muted); }
#lesson .complete-stats b { display: block; margin-top: 4px; font: 800 22px var(--display); letter-spacing: -.05em; }
#lesson .complete-card > p { margin: 16px 0 0; font: 400 10.5px/1.6 var(--sans); color: #4f493c; }
#lesson .complete-actions { display: flex; gap: 8px; margin-top: 22px; }
#lesson .complete-actions button {
  flex: 1;
  padding: 11px 10px;
  border: 1px solid var(--ink);
  background: var(--ink);
  color: var(--paper);
  font: 600 6.5px var(--mono);
  letter-spacing: .05em;
}
#lesson .complete-actions button + button { background: transparent; color: var(--ink); }
#lesson .complete-actions button:hover { background: var(--blue); border-color: var(--blue); color: #fff; }

/* ───────────────────────── quiet mode ───────────────────────── */

#lesson.focus-mode .chapter-spine { display: none; }
#lesson.focus-mode .lesson-view { inset: 70px 0 0; }
#lesson.focus-mode .lesson-head {
  opacity: 1;
  background: var(--ink);
  box-shadow: inset 0 -2px 0 var(--acid);
}
#lesson.focus-mode .lesson-mode-switch { opacity: 1; pointer-events: auto; }
#lesson.focus-mode .read-view { grid-template-columns: minmax(0, 1fr); }
#lesson.focus-mode .reader-margin { display: none; }
#lesson.focus-mode .reader-page {
  max-width: 780px;
  padding-left: clamp(44px, 8vw, 110px);
  padding-right: clamp(44px, 8vw, 110px);
}
#lesson.focus-mode .chapter-ghost { opacity: .4; }
#lesson.focus-mode .lesson-head-left { opacity: .25; }
#lesson.focus-mode .notes-fab, #lesson.focus-mode .notes-backdrop { display: none !important; }
#lesson.focus-mode .lesson-thread { left: max(8px, calc((100% - 780px) / 2 + 8px)); }
#lesson.focus-mode .reader-page blockquote { transform: none; }

/* ───────────────────────── responsive ───────────────────────── */

@media (max-width: 1150px) {
  #lesson .lesson-thread { left: 7px; }
  #lesson .chapter-spine {
    left: 0;
    right: 0;
    top: 70px;
    bottom: auto;
    width: auto;
    height: 46px;
    flex-direction: row;
    align-items: center;
    gap: 19px;
    padding: 0 20px;
    border-right: 0;
    border-bottom: 1px solid var(--ink);
  }
  #lesson .spine-head { display: flex; flex-direction: row; align-items: center; gap: 10px; flex: 0 0 auto; }
  #lesson .spine-label { font-size: 6px; white-space: nowrap; }
  #lesson .spine-head h2, #lesson .spine-head p { display: none; }
  #lesson .course-map {
    display: flex;
    flex: 1;
    margin: 0;
    padding: 0;
    border: 0;
    min-width: 0;
  }
  #lesson .course-map li {
    display: flex;
    gap: 6px;
    align-items: center;
    padding: 0 9px;
    border: 0;
    font-size: 6px;
    white-space: nowrap;
  }
  #lesson .course-map li span {
    width: 19px;
    height: 19px;
    display: grid;
    place-items: center;
    border: 1px solid #a79b83;
    border-radius: 50%;
    font-size: 5.5px;
  }
  #lesson .course-map li b { display: none; }
  #lesson .course-map li.current { margin: 0; padding: 0 9px; background: transparent; color: var(--ink); }
  #lesson .course-map li.current b {
    display: inline;
    max-width: 185px;
    overflow: hidden;
    white-space: nowrap;
    text-overflow: ellipsis;
    font-weight: 600;
  }
  #lesson .course-map li.current span { background: var(--ink); border-color: var(--ink); color: var(--acid); }
  #lesson .course-map li em { display: none; }
  #lesson .course-map li.current b { color: var(--ink); }
  #lesson .spine-outline { display: none; }
  #lesson .chapter-meter { display: none; }
  #lesson .lesson-view { inset: 116px 0 0; }
  #lesson .read-view { grid-template-columns: minmax(0, 1fr) 254px; }
  #lesson .reader-page { padding-left: clamp(42px, 5vw, 64px); padding-right: clamp(42px, 5vw, 64px); }
  #lesson .practice-view { grid-template-columns: 156px minmax(0, 1fr) 232px; }
  #lesson .problem-index { padding-left: 11px; padding-right: 11px; }
  #lesson .problem-stage { margin-right: 14px; padding-left: 27px; padding-right: 27px; }
  #lesson .problem-actions { flex-wrap: wrap; }
  #lesson .problem-actions .next-problem { margin-left: 0; }
  #lesson .scratch-space { padding-left: 12px; padding-right: 12px; }
  #lesson .scratch-space textarea { height: 178px; }
}

@media (max-width: 900px) {
  #lesson .lesson-breadcrumb { display: none; }
  #lesson .lesson-view { inset: 116px 0 0; }
  #lesson .read-view { grid-template-columns: minmax(0, 1fr); }
  #lesson .reader-page { max-width: 860px; }

  #lesson .reader-margin {
    position: fixed;
    z-index: 50;
    top: 116px;
    right: 0;
    bottom: 0;
    width: min(360px, calc(100vw - 30px));
    height: auto;
    min-height: 0;
    visibility: hidden;
    transform: translateX(104%);
    transition: transform .34s cubic-bezier(.2, .8, .2, 1), visibility .34s;
    border-left: 1px solid var(--ink);
    box-shadow: -12px 0 35px rgba(10, 10, 8, .3);
  }
  #lesson.notes-open .reader-margin { visibility: visible; transform: none; }
  #lesson #notesClose { display: grid; }
  #lesson .margin-head-actions button { width: 35px; height: 35px; }
  #lesson .margin-head > div:first-child > b { font-size: 9px; }
  #lesson .note-stack { max-height: 38%; }
  #lesson .thought-board { min-height: 80px; }

  #lesson.practice-mode .chapter-spine { display: none; }
  #lesson.practice-mode .lesson-view { inset: 70px 0 0; }

  #lesson .reader-sidehint {
    display: flex;
    align-items: center;
    gap: 8px;
    margin: -4px 0 24px;
    padding: 8px 0;
    border-top: 1px dashed rgba(20, 19, 14, .24);
    border-bottom: 1px dashed rgba(20, 19, 14, .24);
    font: 400 6.5px/1.5 var(--mono);
    letter-spacing: .03em;
    color: var(--muted);
  }
  #lesson .reader-sidehint span {
    display: grid;
    flex: 0 0 auto;
    place-items: center;
    width: 18px;
    height: 18px;
    border-radius: 50%;
    background: var(--blue);
    color: var(--paper);
    font: 400 10px var(--mono);
  }

  #lesson .notes-fab { display: flex; }
  #lesson .notes-backdrop {
    display: none;
    position: fixed;
    z-index: 45;
    inset: 0;
    background: rgba(10, 10, 8, .52);
    border: 0;
    padding: 0;
  }
  #lesson.notes-open .notes-backdrop { display: block; }
  #lesson.notes-open .notes-fab { opacity: 0; pointer-events: none; }

  #lesson .reader-toc {
    display: flex;
    gap: 0;
    align-items: stretch;
    margin: 0 0 42px;
    border-top: 1px solid var(--line);
    border-bottom: 1px solid var(--line);
    overflow-x: auto;
    scrollbar-width: none;
  }  #lesson .reader-toc::-webkit-scrollbar { display: none; }
  #lesson .reader-toc > span {
    align-self: center;
    padding-right: 10px;
    font: 500 5.5px var(--mono);
    letter-spacing: .14em;
    color: var(--muted);
    white-space: nowrap;
  }
  #lesson .reader-toc button {
    display: grid;
    grid-template-columns: 14px auto;
    gap: 1px 4px;
    padding: 9px 10px;
    border: 0;
    border-left: 1px solid var(--line);
    background: transparent;
    color: var(--ink);
    text-align: left;
    white-space: nowrap;
  }
  #lesson .reader-toc button i { font: 500 5.5px var(--mono); font-style: normal; color: var(--red-ink); }
  #lesson .reader-toc button b { font: 500 6.5px var(--mono); }
  #lesson .reader-toc button em { grid-column: 2; font: 400 5.5px var(--mono); font-style: normal; color: var(--muted); }
  #lesson .reader-toc button:hover { background: rgba(20, 19, 14, .06); }
  #lesson .reader-toc-practice { background: var(--ink); color: var(--paper) !important; }
  #lesson .reader-toc-practice i { color: var(--acid) !important; }
  #lesson .reader-toc-practice em { color: #aaa395 !important; }

  #lesson .thread-percent { display: none; }

  #lesson .practice-view.active { display: flex; flex-direction: column; overflow-y: auto; }
  #lesson .practice-topline { position: sticky; top: 0; flex: 0 0 auto; }
  #lesson .practice-topline-end { display: none; }
  #lesson .problem-index {
    flex: 0 0 auto;
    padding: 0;
    border-right: 0;
    border-bottom: 1px solid #ffffff24;
  }
  #lesson .problem-index > span, #lesson .attempts, #lesson .index-note { display: none; }
  #lesson .problem-path { display: grid; grid-template-columns: repeat(3, 1fr); }
  #lesson .problem-path::before { display: none; }
  #lesson .problem-path button {
    grid-template-columns: 22px minmax(0, 1fr) 12px;
    gap: 5px;
    padding: 10px 12px;
    border: 0;
    border-right: 1px solid #302c24;
    border-bottom: 0;
  }
  #lesson .problem-path button:last-child { border-right: 0; }
  #lesson .problem-path button:hover { padding-left: 12px; }
  #lesson .problem-path button i { width: 20px; height: 20px; }
  #lesson .problem-stage {
    flex: 0 0 auto;
    min-height: 0;
    margin: 13px 14px 0;
    padding: 24px 20px 19px;
    overflow: visible;
    box-shadow: 6px 6px 0 #11100d;
  }
  #lesson .problem-stage h1 { font-size: clamp(33px, 6vw, 45px); }
  #lesson .problem-actions { margin-top: 22px; }
  #lesson .problem-actions .next-problem { margin-left: 0; }
  #lesson .problem-actions .next-problem:disabled { display: none; }
  #lesson .problem-actions.is-solved #hintButton { display: none; }
  #lesson .problem-actions.is-solved .next-problem { grid-column: auto; }
  #lesson .problem-stage { padding-bottom: 17px; }
  #lesson .problem-actions {
    position: sticky;
    z-index: 7;
    bottom: 12px;
    margin: 18px -20px -19px;
    padding: 11px 20px 12px;
    background: var(--paper);
    border-top: 1px solid var(--line);
    box-shadow: 0 -10px 18px rgba(242, 235, 219, .8);
  }
  #lesson .scratch-space {
    flex: 0 0 auto;
    min-height: 0;
    margin: 13px 14px 20px;
    padding: 15px 16px;
    border: 2px solid var(--ink);
    box-shadow: 6px 6px 0 var(--ink);
    overflow: visible;
  }
  #lesson #scratchToggle { display: inline; }
  #lesson .scratch-space:not(.is-open) { padding-bottom: 15px; }
  #lesson .scratch-space:not(.is-open) .scratch-body { display: none; }
  #lesson .scratch-space:not(.is-open) .xp-orb { margin-top: 12px; width: 88px; height: 88px; }
  #lesson .scratch-space textarea { height: 148px; }
  #lesson .xp-orb { width: 92px; height: 92px; margin: 17px 0 0 auto; }
  #lesson .xp-orb b { font-size: 21px; }
  #lesson .practice-keys { display: none; }
}

@media (max-width: 850px) {
  #lesson { height: calc(100vh - 64px); min-height: 650px; }
  #lesson .reader-margin { bottom: 64px; }
  #lesson .notes-fab { bottom: 82px; }
  #lesson .lesson-thread { bottom: 78px; }
  #lesson .practice-complete { inset: 0 0 64px; }
}

@media (max-width: 650px) {
  #lesson {
    height: auto;
    min-height: calc(100vh - 64px);
    overflow: visible;
  }
  #lesson .lesson-head {
    position: relative;
    height: auto;
    grid-template-columns: minmax(0, 1fr) auto;
    grid-template-areas: "left right" "tabs tabs";
    gap: 10px 12px;
    padding: 12px 14px 10px;
  }
  #lesson .lesson-head-left { grid-area: left; gap: 0; }
  #lesson .lesson-brand { font-size: 12px; }
  #lesson .lesson-brand i { display: none; }
  #lesson .lesson-head-right { grid-area: right; gap: 9px; }
  #lesson .lesson-session span { display: none; }
  #lesson .lesson-session b { font-size: 9px; }
  #lesson .quiet-toggle { min-height: 36px; padding: 8px 9px; gap: 4px; }
  #lesson .quiet-toggle b { font-size: 5.5px; }
  #lesson .lesson-mode-switch { grid-area: tabs; width: 100%; }
  #lesson .lesson-mode-switch button { width: 50%; padding: 8px 9px; }
  #lesson .lesson-mode-switch b { font-size: 8.5px; }

  #lesson .chapter-spine {
    position: relative;
    top: auto;
    left: auto;
    right: auto;
    height: 43px;
    gap: 10px;
    padding: 0 14px;
  }
  #lesson .spine-label { font-size: 6px; color: #4d473d; letter-spacing: .1em; }
  #lesson .course-map { overflow: hidden; }
  #lesson .course-map li { padding: 0 5px; }
  #lesson .course-map li span { width: 17px; height: 17px; font-size: 5px; }
  #lesson .course-map li.current b { display: none; }

  #lesson .lesson-view { position: relative; inset: auto; }
  #lesson .read-view.active { display: block; }
  #lesson .theory-reader { height: auto; min-height: 0; overflow: visible; }
  #lesson .reader-progress { height: 3px; }
  #lesson .reader-page {
    max-width: none;
    padding: 31px 18px 56px;
    background-image:
      linear-gradient(90deg, transparent 0 10px, rgba(240, 74, 47, .16) 10px 11px, transparent 11px),
      repeating-linear-gradient(0deg, transparent 0 31px, rgba(20, 19, 14, .04) 31px 32px);
    background-size: auto, 100% 32px;
  }
  #lesson .chapter-ghost { top: 4px; right: -9px; font-size: 132px; }
  #lesson .reader-kicker { gap: 7px; margin-bottom: 15px; font-size: 5.5px; }
  #lesson .reader-kicker i { width: 8px; }
  #lesson .reader-kicker b { display: none; }
  #lesson .reader-page > h1 { font-size: clamp(38px, 11.2vw, 48px); }
  #lesson .reader-lead {
    margin: 26px 0 25px;
    padding-left: 14px;
    font-size: 16.5px;
    line-height: 1.55;
  }
  #lesson .markable.highlighted::before { left: -15px; width: 13px; height: 13px; font-size: 7px; }
  #lesson .theory-rule { gap: 9px; margin: 16px 0 26px; }
  #lesson .theory-rule span { font-size: 10px; }
  #lesson .theory-rule b { font-size: 5.5px; }
  #lesson .reader-toc { margin-bottom: 35px; }
  #lesson .reader-toc > span { display: none; }
  #lesson .reader-toc button { flex: 1; padding: 8px 7px; }
  #lesson .theory-section { display: block; margin: 45px 0; }
  #lesson .section-index { width: 29px; height: 29px; margin-bottom: 12px; font-size: 6px; }
  #lesson .theory-section h2 { margin-top: 0; font-size: 22px; }
  #lesson .theory-section p { font-size: 15.5px; line-height: 1.68; }
  #lesson .riemann-figure { margin-top: 22px; padding: 11px 12px 10px; box-shadow: 4px 4px 0 var(--blue); }
  #lesson .figure-control { grid-template-columns: 1fr 82px; gap: 8px; }
  #lesson .figure-tip { display: none; }
  #lesson .riemann-figure figcaption { font-size: 6px; }
  #lesson .reader-page blockquote {
    grid-template-columns: 30px minmax(0, 1fr);
    margin: 45px 0;
    padding: 25px 18px;
    box-shadow: 5px 5px 0 var(--ink);
  }
  #lesson .reader-page blockquote > span { font-size: 52px; }
  #lesson .reader-page blockquote p { font-size: 22px; line-height: 1.15; }
  #lesson .formula-section { display: block; }
  #lesson .hero-formula { padding: 19px 18px; box-shadow: 6px 6px 0 var(--red); }
  #lesson .hero-formula > b { font-size: clamp(19px, 6vw, 27px); }
  #lesson .formula-steps { gap: 5px; font-size: 5.5px; }
  #lesson .example-block { margin: 46px 0 42px; padding: 18px 17px 20px; box-shadow: 6px 6px 0 var(--ink); }
  #lesson .example-block h3 { font-size: 21px; }
  #lesson .example-block ol { grid-template-columns: 1fr; gap: 12px; }
  #lesson .example-block li { display: grid; grid-template-columns: 15px 1fr; gap: 4px; }
  #lesson .example-block li span { padding-top: 3px; }
  #lesson .example-block li p { margin-top: 0; }
  #lesson .reader-checkpoint { display: block; margin-bottom: 42px; padding: 19px 18px; }
  #lesson .reader-checkpoint h3 { font-size: 20px; }
  #lesson .reader-checkpoint button { margin-top: 16px; }
  #lesson .reader-finish { padding-top: 40px; }
  #lesson .reader-finish h2 { font-size: 34px; }
  #lesson .reader-finish button { width: 100%; }

  #lesson .lesson-thread {
    position: fixed;
    left: 4px;
    top: 163px;
    bottom: 80px;
    width: 17px;
    z-index: 25;
  }
  #lesson .thread-svg { width: 17px; }
  #lesson .thread-knots span { left: 7px; width: 7px; height: 7px; }
  #lesson .thread-bead { left: 7px; width: 10px; height: 10px; }
  #lesson .thread-percent { display: none; }
  #lesson.focus-mode .lesson-thread { left: 4px; top: 124px; }

  #lesson .reader-margin {
    top: auto;
    left: 0;
    right: 0;
    bottom: 64px;
    width: auto;
    height: min(78vh, 620px);
    transform: translateY(106%);
    border-left: 0;
    border-top: 2px solid var(--ink);
    box-shadow: 0 -14px 40px rgba(10, 10, 8, .35);
    overflow-y: auto;
    overscroll-behavior: contain;
  }
  #lesson.notes-open .reader-margin { transform: none; }
  #lesson .note-stack { max-height: 38%; }
  #lesson .thought-board { min-height: 76px; }
  #lesson .margin-head > div:first-child > b { font-size: 9px; }

  #lesson .selection-tool {
    top: auto !important;
    left: 12px !important;
    right: 12px;
    bottom: 80px;
    max-width: none;
    box-shadow: 4px 4px 0 var(--blue);
  }
  #lesson .selection-tool > span { flex: 1; max-width: none; }

  #lesson .quiet-exit.is-visible {
    display: flex;
    position: fixed;
    z-index: 58;
    top: auto;
    bottom: 84px;
    right: 14px;
    width: 50px;
    min-height: 46px;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 3px;
    padding: 7px 5px;
    border: 1px solid var(--ink);
    background: var(--acid);
    color: var(--ink);
    box-shadow: 3px 3px 0 var(--ink);
    font: 500 6.5px var(--mono);
    letter-spacing: .09em;
  }
  #lesson .quiet-exit span { font-size: 13px; line-height: 1; }
  #lesson .quiet-exit b { font: 600 5px var(--mono); letter-spacing: .08em; }

  #lesson .practice-view.active { display: flex; flex-direction: column; overflow: visible; }
  #lesson.practice-mode .lesson-view { position: relative; inset: auto; }
  #lesson .practice-topline { position: sticky; top: 0; height: 44px; padding: 0 10px; }
  #lesson .back-to-theory { font-size: 5.5px; padding: 5px 6px; }
  #lesson .practice-steps { gap: 5px; }
  #lesson .practice-steps b { font-size: 7px; }
  #lesson .problem-path button { grid-template-columns: 20px 1fr; padding: 9px 7px; }
  #lesson .problem-path button em { display: none; }
  #lesson .problem-path button b { font-size: 6.5px; }
  #lesson .problem-stage { margin: 10px 10px 0; padding: 18px 15px 16px; box-shadow: 4px 4px 0 #11100d; }
  #lesson .problem-stage::before { display: none; }
  #lesson .problem-stage h1 { margin: 16px 0 11px; font-size: 31px; }
  #lesson .problem-stage > p { font-size: 11.5px; }
  #lesson .problem-ref { margin-top: 9px; font-size: 5.8px; padding: 5px 6px; }
  #lesson .answer-zone { grid-template-columns: 1fr; gap: 6px; margin: 14px 0 12px; }
  #lesson .choice-answer { min-height: 50px; padding: 9px 11px; }
  #lesson .numeric-answer { font-size: 52px; }
  #lesson .problem-actions { display: grid; grid-template-columns: 1fr 1fr; margin-top: 20px; }
  #lesson .problem-actions #checkAnswer { min-width: 0; }
  #lesson .problem-actions .next-problem { grid-column: 1 / -1; }
  #lesson .problem-actions {
    bottom: 74px;
    margin: 18px -15px -17px;
    padding: 10px 15px 11px;
  }
  #lesson .problem-actions.is-solved .next-problem { grid-column: auto; }
  #lesson .scratch-space { margin: 10px 10px 20px; padding: 14px 14px; box-shadow: 4px 4px 0 var(--ink); }
  #lesson .scratch-space textarea { height: 138px; }
  #lesson .xp-orb { width: 86px; height: 86px; }
  #lesson .practice-complete { position: fixed; inset: 0 0 64px; padding: 12px; }
  #lesson .complete-card { padding: 27px 20px 22px; box-shadow: 7px 7px 0 var(--acid); }
  #lesson .complete-close { width: 32px; height: 32px; }
  #lesson .complete-card h2 { font-size: 31px; }
  #lesson .complete-stats b { font-size: 18px; }
  #lesson .complete-actions { flex-direction: column; }

  #lesson .focus-mode .lesson-view { inset: auto; }
  #lesson .focus-mode .reader-page { padding-left: 27px; padding-right: 18px; }
}

@media (prefers-reduced-motion: reduce) {
  #lesson, #lesson * { animation: none !important; transition-duration: .001ms !important; scroll-behavior: auto !important; }
}