:root {
  color-scheme: dark;
  --bg: #000;
  --surface: #111214;
  --surface-raised: #1c1c1e;
  --surface-soft: #242427;
  --line: #343438;
  --ink: #f5f5f7;
  --muted: #a7a7ad;
  --blue: #2997ff;
  --coral: #ff5a3d;
  --green: #32d074;
  --red: #ff453a;
  --focus: #73b7ff;
  --page-gap: clamp(18px, 5vw, 24px);
  --nav-height: 58px;
  --ease: cubic-bezier(.16, 1, .3, 1);
}

* { box-sizing: border-box; }

html { background: #0a0a0b; -webkit-text-size-adjust: 100%; }

body {
  margin: 0;
  min-height: 100dvh;
  background: #0a0a0b;
  color: var(--ink);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", sans-serif;
  font-size: 17px;
  line-height: 1.45;
  -webkit-font-smoothing: antialiased;
}

button, input { font: inherit; }
button { color: inherit; }

button:focus-visible,
input:focus-visible,
summary:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 3px;
}

[hidden] { display: none !important; }

.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;
}

.skip-link {
  position: fixed;
  z-index: 30;
  left: 12px;
  top: 10px;
  transform: translateY(-160%);
  padding: 10px 14px;
  border-radius: 999px;
  background: var(--ink);
  color: #000;
}

.skip-link:focus { transform: none; }

.app-shell {
  width: min(100%, 430px);
  min-height: 100dvh;
  margin: 0 auto;
  background: var(--bg);
  position: relative;
  overflow: hidden;
  isolation: isolate;
}

.player {
  position: absolute;
  z-index: 20;
  top: 0;
  left: 0;
  right: 0;
  min-height: 58px;
  padding: max(10px, env(safe-area-inset-top)) 14px 8px;
  background: rgba(0, 0, 0, .92);
  border-bottom: 1px solid rgba(255, 255, 255, .1);
  backdrop-filter: saturate(145%) blur(18px);
}

.brand {
  display: inline-flex;
  align-items: baseline;
  min-height: 40px;
  font-size: 22px;
  font-weight: 720;
  letter-spacing: -.03em;
}

.brand span { color: var(--blue); }

.player-controls {
  position: absolute;
  right: 12px;
  top: max(8px, env(safe-area-inset-top));
  display: flex;
  min-height: 44px;
  align-items: center;
  gap: 2px;
}

.player.has-controls .brand { visibility: hidden; }
.player.has-controls .player-controls {
  left: 8px;
  right: 8px;
  justify-content: space-between;
}

.icon-button,
.text-button,
.player-speed,
.skip-button {
  min-width: 44px;
  min-height: 44px;
  border: 0;
  border-radius: 999px;
  background: transparent;
  color: var(--ink);
  cursor: pointer;
}

.icon-button:disabled,
.text-button:disabled,
.player-speed:disabled,
.skip-button:disabled { opacity: .36; cursor: default; }

.icon-button:hover:not(:disabled),
.text-button:hover:not(:disabled),
.player-speed:hover:not(:disabled),
.skip-button:hover:not(:disabled) { background: rgba(255, 255, 255, .08); }

.icon-button svg { width: 22px; height: 22px; fill: currentColor; stroke: currentColor; stroke-width: 1.5; }
.icon-button .pause-glyph { display: none; }
.player.is-playing .icon-button .play-glyph { display: none; }
.player.is-playing .icon-button .pause-glyph { display: block; }
.icon-button .sound-wave { fill: none; }
.player.is-muted .sound-wave { display: none; }

.text-button,
.player-speed,
.skip-button { padding: 0 10px; font-size: 13px; font-weight: 650; }
.player-speed { padding-inline: 8px; font-variant-numeric: tabular-nums; }
.skip-button { color: var(--blue); }

.media-row {
  position: relative;
  display: grid;
  grid-template-columns: 34px 1fr 34px;
  gap: 8px;
  align-items: center;
  padding-top: 4px;
}

.player-feedback {
  position: absolute;
  inset: 2px 0 0;
  min-height: 22px;
  display: grid;
  place-items: center;
  padding: 0 10px;
  background: #000;
  color: var(--muted);
  font-size: 12px;
  font-weight: 600;
  text-align: center;
}

.player-feedback[data-tone="error"] { color: #ff8d85; }
.player-feedback[data-tone="loading"] { color: var(--ink); }

.player[data-media-state="loading"] #play-pause { cursor: progress; }
.player[data-media-state="loading"] #play-pause svg {
  animation: player-loading 1s linear infinite;
  opacity: .72;
}

.player[data-media-state="error"] #play-pause { color: var(--red); }

@keyframes player-loading { to { transform: rotate(360deg); } }

.media-row output {
  font-variant-numeric: tabular-nums;
  color: var(--muted);
  font-size: 11px;
  text-align: center;
}

#scrubber {
  --filled: 0%;
  width: 100%;
  height: 22px;
  margin: 0;
  appearance: none;
  background: transparent;
  cursor: pointer;
  touch-action: pan-y;
  user-select: none;
}

#scrubber::-webkit-slider-runnable-track {
  height: 4px;
  border-radius: 999px;
  background: linear-gradient(90deg, #fff 0 var(--filled), #3a3a3e var(--filled) 100%);
}

#scrubber::-webkit-slider-thumb {
  appearance: none;
  width: 14px;
  height: 14px;
  margin-top: -5px;
  border: 0;
  border-radius: 50%;
  background: #fff;
}

#scrubber::-moz-range-track { height: 4px; border-radius: 999px; background: #3a3a3e; }
#scrubber::-moz-range-progress { height: 4px; border-radius: 999px; background: #fff; }
#scrubber::-moz-range-thumb { width: 14px; height: 14px; border: 0; border-radius: 50%; background: #fff; }

.top-progress {
  position: absolute;
  bottom: -1px;
  left: 0;
  right: 0;
  height: 2px;
  background: #1c1c1e;
  overflow: hidden;
}

.top-progress span {
  display: block;
  width: 100%;
  height: 100%;
  background: var(--blue);
  transform: scaleX(0);
  transform-origin: left center;
  transition: transform .45s var(--ease);
}

.lesson {
  height: 100dvh;
  padding-top: calc(58px + env(safe-area-inset-top));
  padding-bottom: calc(var(--nav-height) + env(safe-area-inset-bottom));
  position: relative;
  overflow: hidden;
}

.lesson-page {
  position: absolute;
  inset: calc(58px + env(safe-area-inset-top)) 0 calc(var(--nav-height) + env(safe-area-inset-bottom));
  background: var(--bg);
  overflow: hidden;
  transform: translate3d(0, 0, 0);
  opacity: 1;
}

.lesson-page.is-entering-forward { animation: page-in-forward .62s var(--ease) both; }
.lesson-page.is-entering-backward { animation: page-in-backward .62s var(--ease) both; }
.lesson-page.is-leaving-forward { animation: page-out-forward .62s var(--ease) both; }
.lesson-page.is-leaving-backward { animation: page-out-backward .62s var(--ease) both; }

@keyframes page-in-forward { from { transform: translate3d(0, 46px, 0); opacity: 0; } }
@keyframes page-out-forward { to { transform: translate3d(0, -34px, 0); opacity: 0; } }
@keyframes page-in-backward { from { transform: translate3d(0, -34px, 0); opacity: 0; } }
@keyframes page-out-backward { to { transform: translate3d(0, 46px, 0); opacity: 0; } }

.page-scroll {
  height: 100%;
  overflow-y: auto;
  overscroll-behavior: contain;
  scrollbar-width: thin;
  scrollbar-color: #414145 transparent;
  padding: 34px var(--page-gap) 108px;
}

.lesson-page:not(.is-active) { pointer-events: none; }

h1, h2, h3, p { margin-top: 0; }
h1 { margin-bottom: 14px; font-size: clamp(38px, 11vw, 52px); line-height: .98; letter-spacing: -.04em; text-wrap: balance; }
h2 { margin: 0; font-size: 30px; line-height: 1.08; letter-spacing: -.03em; text-wrap: balance; }
h3 { font-size: 25px; letter-spacing: -.025em; }
.lead { max-width: 34ch; margin-bottom: 30px; color: var(--muted); font-size: 19px; line-height: 1.42; text-wrap: pretty; }
.intro-label { margin-bottom: 12px; color: var(--muted); font-size: 13px; }

.hero-mark {
  min-height: 154px;
  margin-bottom: 32px;
  display: grid;
  grid-template-columns: 1fr 38px 1fr;
  align-items: center;
  color: var(--ink);
}

.hero-log { font-size: 58px; font-weight: 720; letter-spacing: -.05em; }
.hero-question { color: var(--coral); font-size: 54px; text-align: center; }
.hero-power { justify-self: end; font-size: 28px; font-weight: 650; font-variant-numeric: tabular-nums; }
.hero-power sup { color: var(--coral); }

.prediction,
.action-block {
  margin-top: 24px;
  padding-top: 20px;
  border-top: 1px solid var(--line);
}

.prediction p,
.action-block p { margin-bottom: 14px; }
.formula-large { margin: 18px 0 20px; font-size: 29px; }

.choice-stack,
.choice-row { display: flex; gap: 10px; }
.choice-stack { flex-direction: column; }
.choice-row { flex-wrap: wrap; }

.choice {
  min-height: 48px;
  padding: 11px 16px;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--surface);
  color: var(--ink);
  cursor: pointer;
  text-align: left;
  transition: border-color .2s, background .2s, transform .2s var(--ease);
}

.choice:hover:not(:disabled) { border-color: #67676d; transform: translateY(-1px); }
.choice:disabled { cursor: default; opacity: .55; }
.choice.is-selected { border-color: var(--blue); background: #0b2840; }
.choice.is-correct { border-color: var(--green); background: #082718; opacity: 1; }
.choice.is-wrong { border-color: var(--red); background: #32110f; opacity: 1; }
.math-choice { text-align: center; font-size: 19px; }

.local-feedback { min-height: 44px; margin: 14px 0 0; color: var(--muted); font-size: 15px; }
.local-feedback.is-success { color: #70e69c; }
.local-feedback.is-error { color: #ff8d85; }
.feedback-math {
  display: block;
  max-width: 100%;
  margin-top: 10px;
  overflow-x: auto;
  color: var(--ink);
  font-size: 16px;
  scrollbar-width: thin;
}
.feedback-math .katex-display { margin: 0; text-align: left; }

.start-actions { display: grid; gap: 10px; margin-top: 24px; }
.baseline-continue { width: 100%; margin-top: 4px; }
.primary,
.secondary,
.why-button {
  min-height: 50px;
  padding: 12px 18px;
  border-radius: 999px;
  font-weight: 700;
  cursor: pointer;
}

.primary { border: 0; background: var(--blue); color: #001322; }
.primary:hover:not(:disabled) { background: #53aaff; }
.primary:disabled { opacity: .42; cursor: default; }
.secondary { border: 1px solid var(--line); background: transparent; color: var(--ink); }
.why-button { min-height: 44px; padding: 8px 14px; border: 0; background: transparent; color: var(--blue); }
.next-action { width: 100%; margin-top: 22px; }
.result-note { margin: 18px 0 0; color: var(--muted); font-size: 13px; }

.step-heading { display: flex; gap: 14px; align-items: flex-start; margin-bottom: 26px; }
.step-heading > span {
  flex: 0 0 34px;
  height: 34px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--surface-soft);
  color: var(--muted);
  font-size: 14px;
  font-weight: 700;
}

.math-stage {
  min-height: 326px;
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 18px;
  padding: 22px 0;
  overflow: hidden;
}

.lesson-page.is-attention-mode .step-heading,
.lesson-page.is-attention-mode .next-action,
.lesson-page.is-attention-mode .action-block {
  display: none !important;
}

.lesson-page.is-attention-mode.has-live-action .action-block:not([hidden]) {
  display: block !important;
  animation: attention-in .48s var(--ease) both;
}

.math-stage.is-attention-mode {
  min-height: min(58dvh, 520px);
  padding-block: 8px;
}

.math-stage.is-attention-mode > :not(.narration-focus) {
  display: none !important;
}

.narration-focus {
  position: relative;
  width: 100%;
  min-height: min(52dvh, 460px);
  display: grid;
  align-items: center;
  justify-items: stretch;
}

.narration-focus[hidden] { display: none !important; }

.narration-focus__content {
  width: 100%;
  max-width: 620px;
  justify-self: center;
  display: grid;
  justify-items: stretch;
  gap: 14px;
  animation: attention-in .48s var(--ease) both;
}

.narration-focus__content:empty { min-height: 1px; }

.narration-focus__content > span:not(.derivation-step),
.narration-focus__content > div:not(.notation-source):not(.power-readout):not(.equivalence):not(.machine-pair):not(.exponent-join):not(.operation-map):not(.factor-groups):not(.factor-combined):not(.proof-role-map):not(.proof-definitions):not(.proof-derivation):not(.rule-formula):not(.condition-summary):not(.condition-case):not(.general-definition):not(.trap-comparison):not(.definition-test):not(.power-operation-proof):not(.rule-boundary):not(.transfer-map) {
  min-height: 72px;
  display: grid;
  place-items: center;
  gap: 6px;
  padding: 14px;
  border-radius: 16px;
  background: var(--surface-soft);
  text-align: center;
}

.narration-focus__content > span > small { color: var(--muted); font-size: 11px; }
.narration-focus__content > span > strong { display: flex; align-items: center; justify-content: center; gap: 7px; font-size: 22px; }
.narration-focus__content > span > strong b { color: var(--blue); }
.narration-focus__content > span > strong i { color: var(--ink); font-style: normal; }

@keyframes attention-in {
  from { opacity: 0; transform: translateY(12px) scale(.985); }
  to { opacity: 1; transform: translateY(0) scale(1); }
}

.formula-morph {
  width: 100%;
  display: grid;
  gap: 12px;
}

.morph-eyebrow {
  margin: 0;
  color: var(--muted);
  font-size: 11px;
  font-weight: 720;
  letter-spacing: .055em;
  text-align: center;
  text-transform: uppercase;
}

.morph-board {
  width: 100%;
  min-height: 260px;
  display: grid;
  align-content: center;
  gap: 16px;
  padding: 20px 16px;
  border: 1px solid rgba(255, 255, 255, .1);
  border-radius: 22px;
  background:
    radial-gradient(circle at 50% 0%, rgba(41, 151, 255, .1), transparent 44%),
    rgba(17, 18, 20, .92);
  box-shadow: 0 22px 70px rgba(0, 0, 0, .34);
}

.morph-equations {
  display: grid;
  gap: 10px;
}

.morph-equation {
  min-width: 0;
  min-height: 62px;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 12px;
  border-radius: 15px;
  background: rgba(255, 255, 255, .045);
  color: var(--ink);
  font-family: KaTeX_Main, "Times New Roman", serif;
  font-size: clamp(21px, 6.2vw, 27px);
  line-height: 1.2;
}

.morph-equation-hero {
  min-height: 92px;
  font-size: clamp(28px, 9vw, 38px);
}

.morph-token {
  display: inline-flex;
  align-items: baseline;
  justify-content: center;
  min-width: .35em;
  transform-origin: center;
  will-change: transform, opacity;
}

.morph-token .katex { color: inherit; font-size: 1em; }
.role-base { color: var(--blue); }
.role-target { color: var(--coral); }
.role-exponent { color: #c59bff; }
.role-neutral { color: var(--ink); }

.morph-log-term,
.morph-power-term {
  display: inline-flex;
  align-items: baseline;
  white-space: nowrap;
}

.morph-fraction-term {
  min-width: 70px;
  display: inline-grid;
  grid-template-rows: auto 1px auto;
  justify-items: center;
  align-items: center;
  gap: 4px;
  line-height: 1;
}

.morph-fraction-part {
  min-height: 1.05em;
  display: inline-flex;
  align-items: baseline;
}

.morph-fraction-line {
  width: 100%;
  min-width: 62px;
  height: 1px;
  background: currentColor;
}

.morph-log-word {
  margin-right: 1px;
  letter-spacing: -.035em;
}

.morph-log-term sub {
  align-self: flex-end;
  margin: 0 2px 1px 0;
  font-size: .58em;
  line-height: 1;
}

.morph-power-term > sup,
.morph-combined-exponent {
  align-self: flex-start;
  display: inline-flex;
  align-items: baseline;
  gap: 1px;
  margin-left: 1px;
  font-size: .58em;
  line-height: 1;
}

.morph-bridge { margin-inline: 4px; color: var(--muted); }
.morph-exponent-operation { padding-inline: 1px; }

.encoding-legend {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 7px;
}

.encoding-chip {
  min-width: 0;
  min-height: 56px;
  display: grid;
  align-content: center;
  justify-items: center;
  gap: 3px;
  padding: 7px 9px;
  border: 1px solid rgba(255, 255, 255, .075);
  border-radius: 13px;
  background: rgba(255, 255, 255, .045);
}

.encoding-chip small {
  color: var(--muted);
  font-size: 9px;
  font-weight: 650;
  line-height: 1.2;
  text-align: center;
}

.encoding-chip strong {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  color: inherit;
  font-size: 17px;
  font-weight: 650;
}

.encoding-chip:only-child { grid-column: 2; }

.encoding-arrow { color: var(--muted); font-family: inherit; }

.morph-note,
.morph-causal-line {
  max-width: 520px;
  margin: 0 auto;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.4;
  text-align: center;
  text-wrap: pretty;
}

.morph-causal-line {
  padding: 9px 11px;
  border-radius: 12px;
  background: rgba(41, 151, 255, .09);
  color: #cae7ff;
}

.morph-concrete-anchor {
  width: 100%;
  min-width: 0;
  max-width: 100%;
  overflow: visible;
  display: grid;
  justify-items: center;
  gap: 5px;
  padding-top: 4px;
  color: var(--ink);
  font-size: 19px;
}

.morph-concrete-anchor small {
  color: var(--muted);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", sans-serif;
  font-size: 10px;
}

.morph-concrete-anchor .katex { max-width: 100%; font-size: clamp(11px, 3.4vw, 16px); }

.morph-rule-row {
  flex-wrap: nowrap;
  overflow-x: auto;
  justify-content: center;
  font-size: clamp(19px, 6.8vw, 29px);
}

.morph-ghost {
  position: absolute !important;
  z-index: 4;
  margin: 0 !important;
  pointer-events: none;
  transform-origin: center;
  will-change: transform, opacity;
}

@media (max-width: 360px) {
  .morph-board { min-height: 248px; padding: 16px 11px; }
  .morph-equation { gap: 6px; padding-inline: 8px; font-size: 20px; }
  .morph-equation-hero { font-size: 26px; }
  .encoding-legend { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

.notation-unpack {
  display: grid;
  gap: 12px;
  padding: 14px;
  border-radius: 14px;
  background: var(--surface);
  animation: proof-in .52s var(--ease) both;
}

.notation-source { color: var(--ink); font-size: 28px; text-align: center; }
.notation-roles {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px;
}
.notation-roles > span {
  min-width: 0;
  min-height: 64px;
  display: grid;
  grid-template-columns: auto 1fr;
  align-items: center;
  gap: 8px;
  padding: 10px;
  border-radius: 12px;
  background: var(--surface-soft);
}
.notation-roles strong { color: var(--coral); font-size: 20px; }
.notation-roles small { color: var(--muted); font-size: 11px; line-height: 1.3; }
.power-question {
  display: grid;
  justify-items: center;
  gap: 6px;
  padding-top: 12px;
  border-top: 1px solid var(--line);
  animation: proof-in .52s var(--ease) both;
}
.power-question small { color: var(--muted); font-size: 11px; }
.power-question strong { color: var(--ink); font-size: 24px; }

.equivalence {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 12px;
  min-height: 62px;
  color: var(--muted);
  opacity: 0;
  transform: translateY(10px);
  transition: opacity .45s, transform .65s var(--ease);
}

.meaning-stage.cue--unlock-exponent .equivalence,
.meaning-stage.cue--confirm-three .equivalence,
.meaning-stage.cue--show-general-definition .equivalence,
.meaning-stage.cue--compress-meaning .equivalence { opacity: 1; transform: none; color: var(--ink); }

.role-map,
.condition-summary,
.proof-role-map {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 7px;
  animation: proof-in .52s var(--ease) both;
}

.role-map > span,
.condition-summary > span,
.proof-role-map > span {
  min-width: 0;
  min-height: 62px;
  display: grid;
  align-content: center;
  justify-items: center;
  gap: 5px;
  padding: 8px 6px;
  border-radius: 12px;
  background: var(--surface-soft);
  text-align: center;
}
.role-map small,
.condition-summary small,
.proof-role-map small { color: var(--muted); font-size: 10px; line-height: 1.2; }
.role-map strong,
.proof-role-map strong { display: flex; align-items: center; justify-content: center; gap: 5px; font-size: 17px; }
.role-map i,
.proof-role-map i { color: var(--ink); font-style: normal; }
.role-map b { color: var(--blue); font-weight: 650; }
.condition-summary strong { color: var(--green); font-size: 16px; }

.general-definition,
.symbolic-proof,
.definition-test,
.power-operation-proof {
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--surface);
}

.general-definition {
  display: grid;
  justify-items: center;
  gap: 10px;
  padding: 16px;
  animation: proof-in .58s var(--ease) both;
}

.proof-kicker {
  color: var(--muted);
  font-size: 11px;
  font-weight: 760;
  letter-spacing: .06em;
  text-transform: uppercase;
}

.definition-formula { width: 100%; font-size: 21px; text-align: center; }
.definition-formula .katex-display { margin: 0; }

.condition-lab { animation: proof-in .52s var(--ease) both; }
.condition-case {
  display: grid;
  justify-items: center;
  gap: 12px;
  padding: 15px;
  border-radius: 14px;
  background: var(--surface);
  text-align: center;
}
.condition-case > small { color: var(--muted); font-size: 11px; }
.condition-examples { display: flex; flex-wrap: wrap; justify-content: center; gap: 7px; width: 100%; }
.condition-examples > span {
  min-height: 42px;
  display: grid;
  place-items: center;
  padding: 7px 9px;
  border-radius: 10px;
  background: var(--surface-soft);
  color: var(--ink);
  font-size: 15px;
}
.condition-case p { margin: 0; color: var(--muted); font-size: 13px; line-height: 1.35; text-wrap: pretty; }
.condition-case > strong { display: flex; align-items: center; gap: 8px; font-size: 13px; }
.condition-case > strong span { color: var(--muted); font-weight: 650; }
.condition-case > strong i { color: var(--green); font-size: 18px; font-style: normal; }

.proof-conditions {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 6px;
}

.proof-conditions > span {
  min-height: 30px;
  display: grid;
  place-items: center;
  gap: 2px;
  padding: 4px 9px;
  border-radius: 999px;
  background: var(--surface-soft);
  color: var(--muted);
  font-size: 13px;
}
.proof-conditions small { font-size: 9px; line-height: 1; }
.proof-conditions b { color: var(--ink); font-size: 12px; font-weight: 650; }

@keyframes proof-in {
  from { opacity: 0; transform: translateY(10px) scale(.985); }
  to { opacity: 1; transform: none; }
}

.power-readout { display: flex; justify-content: center; align-items: baseline; gap: 7px; font-size: 30px; font-variant-numeric: tabular-nums; }
.power-base sup { color: var(--coral); font-size: .62em; }
.power-readout strong:last-child { color: var(--blue); }

.power-dots { display: flex; flex-wrap: wrap; justify-content: center; gap: 6px; min-height: 18px; }
.power-dots i { width: 12px; height: 12px; border-radius: 50%; background: var(--blue); }

.action-block label { display: block; margin-bottom: 14px; }
#exponent-slider { width: 100%; accent-color: var(--coral); min-height: 44px; }
.range-labels { display: flex; justify-content: space-between; color: var(--muted); font-size: 12px; font-variant-numeric: tabular-nums; }

.machine-pair { display: flex; gap: 10px; }
.mini-machine {
  flex: 1;
  min-width: 0;
  min-height: 80px;
  padding: 12px;
  display: grid;
  grid-template-columns: 1fr auto;
  align-items: center;
  gap: 4px;
  border-radius: 14px;
  background: var(--surface);
  opacity: 0;
  transform: translateY(12px);
  transition: opacity .45s, transform .65s var(--ease);
}
.mini-machine i { grid-row: 2; color: var(--blue); font-style: normal; }
.mini-machine strong { grid-row: 1 / 3; grid-column: 2; color: var(--coral); font-size: 27px; }

.sum-stage.cue--show-two-machines .mini-machine,
.sum-stage.cue--join-exponents .mini-machine,
.sum-stage.cue--ask-sum-inside .mini-machine,
.sum-stage.cue--multiply-inputs .mini-machine,
.sum-stage.cue--expand-sum-factors .mini-machine,
.sum-stage.cue--merge-sum-factors .mini-machine,
.sum-stage.cue--show-sum-rule .mini-machine,
.difference-stage.cue--show-quotient-powers .mini-machine,
.difference-stage.cue--show-factor-counts .mini-machine,
.difference-stage.cue--remove-exponents .mini-machine,
.difference-stage.cue--ask-difference-inside .mini-machine,
.difference-stage.cue--divide-inputs .mini-machine,
.difference-stage.cue--expand-quotient-factors .mini-machine,
.difference-stage.cue--cancel-quotient-factors .mini-machine,
.difference-stage.cue--show-difference-rule .mini-machine { opacity: 1; transform: none; }

.exponent-join {
  display: flex;
  justify-content: center;
  gap: 10px;
  align-items: baseline;
  font-size: 28px;
  opacity: 0;
  transform: scale(.92);
  transition: opacity .4s, transform .6s var(--ease);
}
.exponent-join strong:last-child { color: var(--green); }
.sum-stage.cue--join-exponents .exponent-join,
.sum-stage.cue--ask-sum-inside .exponent-join,
.sum-stage.cue--multiply-inputs .exponent-join,
.sum-stage.cue--expand-sum-factors .exponent-join,
.sum-stage.cue--merge-sum-factors .exponent-join,
.sum-stage.cue--show-sum-rule .exponent-join { opacity: 1; transform: none; }

.operation-map {
  display: flex;
  justify-content: center;
  align-items: center;
  gap: 10px;
  min-height: 62px;
  font-size: 25px;
  font-variant-numeric: tabular-nums;
}
.map-input, .map-result { min-width: 46px; padding: 8px 10px; border-radius: 10px; background: var(--surface); text-align: center; }
.map-operation { color: var(--coral); font-size: 30px; }
.map-result { color: var(--green); }

.factor-proof,
.rule-formula {
  opacity: 0;
  transform: translateY(10px);
  transition: opacity .45s, transform .65s var(--ease);
}
.rule-formula { font-size: 21px; text-align: center; }
.sum-stage.cue--expand-sum-factors .factor-proof,
.sum-stage.cue--merge-sum-factors .factor-proof,
.sum-stage.cue--name-sum-symbols .factor-proof,
.sum-stage.cue--prove-sum-symbolically .factor-proof,
.sum-stage.cue--show-sum-rule .factor-proof,
.sum-stage.cue--show-sum-rule .rule-formula,
.difference-stage.cue--expand-quotient-factors .factor-proof,
.difference-stage.cue--cancel-quotient-factors .factor-proof,
.difference-stage.cue--name-difference-symbols .factor-proof,
.difference-stage.cue--prove-difference-symbolically .factor-proof,
.difference-stage.cue--show-difference-rule .factor-proof,
.difference-stage.cue--show-difference-rule .rule-formula { opacity: 1; transform: none; }

.factor-proof { display: grid; gap: 14px; color: var(--muted); }
.factor-groups {
  display: grid;
  grid-template-columns: minmax(0, 3fr) 22px minmax(0, 2fr);
  align-items: center;
  gap: 8px;
  transition: opacity .45s, transform .65s var(--ease);
}
.factor-group { min-width: 0; display: grid; justify-items: center; gap: 6px; }
.factor-title { color: var(--ink); font-size: 21px; }
.factor-note { color: var(--muted); font-size: 12px; line-height: 1.2; text-align: center; }
.factor-between { color: var(--coral); font-size: 24px; text-align: center; }
.factor-chain { display: flex; justify-content: center; align-items: center; gap: 5px; min-width: 0; }
.factor-chain i {
  position: relative;
  flex: 0 0 30px;
  width: 30px;
  height: 30px;
  display: grid;
  place-items: center;
  border-radius: 9px;
  background: var(--surface-soft);
  color: var(--ink);
  font-style: normal;
  font-size: 15px;
  font-weight: 750;
  font-variant-numeric: tabular-nums;
  transition: opacity .4s, transform .6s var(--ease), background .4s;
}
.factor-chain b { color: #73737b; font-size: 14px; font-weight: 650; }
.factor-group-left .factor-chain i,
.factor-chain-five i:nth-of-type(-n+3) { background: var(--coral); color: #190401; }
.factor-group-right .factor-chain i,
.factor-chain-five i:nth-of-type(n+4) { background: var(--blue); color: #001322; }
.factor-combined,
.factor-remainder {
  display: grid;
  justify-items: center;
  gap: 8px;
  opacity: 0;
  transform: translateY(10px) scale(.98);
  transition: opacity .45s, transform .65s var(--ease);
}
.factor-compressed { color: var(--ink); font-size: 18px; }
.sum-stage.cue--merge-sum-factors .factor-groups,
.sum-stage.cue--show-sum-rule .factor-groups { opacity: .54; transform: scale(.97); }
.sum-stage.cue--merge-sum-factors .factor-combined,
.sum-stage.cue--name-sum-symbols .factor-combined,
.sum-stage.cue--prove-sum-symbolically .factor-combined,
.sum-stage.cue--show-sum-rule .factor-combined { opacity: 1; transform: none; }

.factor-fraction { width: min(100%, 262px); margin: 0 auto; display: grid; justify-items: center; gap: 7px; }
.factor-fraction-line { width: 100%; height: 1px; background: #74747b; }
.factor-numerator i { background: var(--coral); color: #190401; }
.factor-numerator i.is-cancelled,
.factor-denominator i.is-cancelled { background: #16314b; color: var(--ink); }
.factor-chain i.is-cancelled::after {
  content: "";
  position: absolute;
  width: 38px;
  height: 2px;
  border-radius: 999px;
  background: var(--red);
  transform: rotate(-42deg) scaleX(0);
  transition: transform .55s var(--ease);
}
.difference-stage.cue--cancel-quotient-factors .factor-chain i.is-cancelled,
.difference-stage.cue--name-difference-symbols .factor-chain i.is-cancelled,
.difference-stage.cue--prove-difference-symbolically .factor-chain i.is-cancelled,
.difference-stage.cue--show-difference-rule .factor-chain i.is-cancelled { opacity: .3; transform: scale(.9); }
.difference-stage.cue--cancel-quotient-factors .factor-chain i.is-cancelled::after,
.difference-stage.cue--name-difference-symbols .factor-chain i.is-cancelled::after,
.difference-stage.cue--prove-difference-symbolically .factor-chain i.is-cancelled::after,
.difference-stage.cue--show-difference-rule .factor-chain i.is-cancelled::after { transform: rotate(-42deg) scaleX(1); }
.difference-stage.cue--cancel-quotient-factors .factor-remainder,
.difference-stage.cue--name-difference-symbols .factor-remainder,
.difference-stage.cue--prove-difference-symbolically .factor-remainder,
.difference-stage.cue--show-difference-rule .factor-remainder { opacity: 1; transform: none; }

.symbolic-proof {
  display: grid;
  gap: 12px;
  padding: 16px;
  animation: proof-in .58s var(--ease) both;
}

.proof-role-map { grid-template-columns: 1fr; }
.proof-role-map > span {
  min-height: 46px;
  grid-template-columns: minmax(84px, .8fr) 1.2fr;
  justify-items: start;
  text-align: left;
}
.proof-role-map strong { justify-content: flex-start; }

.proof-definitions {
  display: grid;
  grid-template-columns: 1fr;
  gap: 8px;
}

.proof-definitions > span {
  min-width: 0;
  min-height: 52px;
  display: grid;
  place-items: center;
  gap: 5px;
  padding: 9px;
  border-radius: 12px;
  background: var(--surface-soft);
  color: var(--ink);
  font-size: 15px;
  text-align: center;
}
.proof-definitions > span > small { color: var(--muted); font-size: 12px; }
.proof-definitions > span > b { color: var(--ink); font-size: 15px; font-weight: 500; }

.proof-derivation {
  min-width: 0;
  overflow-x: auto;
  display: grid;
  gap: 7px;
  color: var(--ink);
  font-size: 17px;
  text-align: center;
}
.proof-derivation .katex-display { margin: 0; }
.derivation-step,
.derivation-note {
  opacity: 0;
  transform: translateY(7px);
  transition: opacity .38s, transform .58s var(--ease);
}
.derivation-step {
  min-height: 48px;
  display: grid;
  place-items: center;
  padding: 8px;
  border-radius: 12px;
  background: #161719;
}
.derivation-note { color: var(--muted); font-size: 11px; line-height: 1.3; text-wrap: pretty; }
.derivation-step.is-visible,
.derivation-note.is-visible { opacity: 1; transform: none; }

.proof-conclusion {
  max-width: 100%;
  overflow-x: auto;
  padding-top: 12px;
  border-top: 1px solid var(--line);
  color: var(--green);
}

.sum-stage.cue--name-sum-symbols .factor-proof,
.sum-stage.cue--prove-sum-symbolically .factor-proof,
.sum-stage.cue--show-sum-rule .factor-proof,
.difference-stage.cue--name-difference-symbols .factor-proof,
.difference-stage.cue--prove-difference-symbolically .factor-proof,
.difference-stage.cue--show-difference-rule .factor-proof {
  opacity: .32;
  transform: scale(.975);
}

.exponent-stack {
  display: grid;
  gap: 10px;
  opacity: 0;
  transform: translateY(10px);
  transition: opacity .45s, transform .65s var(--ease);
}
.difference-stage.cue--show-factor-counts .exponent-stack,
.difference-stage.cue--remove-exponents .exponent-stack,
.difference-stage.cue--ask-difference-inside .exponent-stack,
.difference-stage.cue--divide-inputs .exponent-stack,
.difference-stage.cue--expand-quotient-factors .exponent-stack,
.difference-stage.cue--cancel-quotient-factors .exponent-stack,
.difference-stage.cue--name-difference-symbols .exponent-stack,
.difference-stage.cue--prove-difference-symbolically .exponent-stack,
.difference-stage.cue--show-difference-rule .exponent-stack { opacity: 1; transform: none; }
.stack-equation { color: var(--ink); text-align: center; font-size: 17px; }
.stack-row { display: flex; justify-content: center; gap: 8px; }
.stack-row i { width: 34px; height: 34px; display: grid; place-items: center; border-radius: 10px; background: var(--blue); color: #001322; font-style: normal; font-weight: 750; transition: opacity .35s, transform .55s var(--ease); }
.stack-label { display: flex; flex-wrap: wrap; justify-content: center; gap: 6px 12px; color: var(--muted); font-size: 13px; font-variant-numeric: tabular-nums; }
.stack-label strong { color: var(--green); opacity: 0; }
.difference-stage.cue--remove-exponents .stack-row i:nth-last-child(-n+2),
.difference-stage.cue--ask-difference-inside .stack-row i:nth-last-child(-n+2),
.difference-stage.cue--divide-inputs .stack-row i:nth-last-child(-n+2),
.difference-stage.cue--expand-quotient-factors .stack-row i:nth-last-child(-n+2),
.difference-stage.cue--cancel-quotient-factors .stack-row i:nth-last-child(-n+2),
.difference-stage.cue--name-difference-symbols .stack-row i:nth-last-child(-n+2),
.difference-stage.cue--prove-difference-symbolically .stack-row i:nth-last-child(-n+2),
.difference-stage.cue--show-difference-rule .stack-row i:nth-last-child(-n+2) { opacity: .15; transform: translateY(-8px) scale(.78); }
.difference-stage.cue--remove-exponents .stack-label strong,
.difference-stage.cue--ask-difference-inside .stack-label strong,
.difference-stage.cue--divide-inputs .stack-label strong,
.difference-stage.cue--expand-quotient-factors .stack-label strong,
.difference-stage.cue--cancel-quotient-factors .stack-label strong,
.difference-stage.cue--name-difference-symbols .stack-label strong,
.difference-stage.cue--prove-difference-symbolically .stack-label strong,
.difference-stage.cue--show-difference-rule .stack-label strong { opacity: 1; }

.trap-comparison { display: grid; grid-template-columns: 1fr 34px 1fr; align-items: center; gap: 8px; }
.trap-comparison > div { min-height: 112px; display: grid; place-items: center; align-content: center; gap: 12px; padding: 12px; border-radius: 14px; background: var(--surface); }
.trap-comparison strong { min-height: 28px; color: var(--coral); font-variant-numeric: tabular-nums; }
.comparison-sign { text-align: center; color: var(--muted); font-size: 28px; }

.definition-test {
  display: grid;
  justify-items: center;
  gap: 10px;
  padding: 15px;
  color: var(--ink);
  text-align: center;
  animation: proof-in .58s var(--ease) both;
}
.definition-test strong { color: var(--red); font-size: 23px; }

.power-operation-proof {
  display: grid;
  grid-template-columns: 1fr;
  gap: 8px;
  padding: 12px;
  animation: proof-in .58s var(--ease) both;
}
.power-operation-proof > div {
  display: grid;
  gap: 5px;
  padding: 11px;
  border-radius: 12px;
  background: var(--surface);
}
.power-operation-proof small { color: var(--muted); font-size: 11px; }
.power-operation-proof .is-valid { border: 1px solid rgba(50, 208, 116, .42); }
.power-operation-proof .is-invalid { border: 1px solid rgba(255, 69, 58, .42); }
.power-operation-proof .is-valid > span { color: var(--green); }
.power-operation-proof .is-invalid > span { color: #ff8d85; }

.false-rule {
  position: relative;
  min-height: 54px;
  display: grid;
  place-items: center;
  color: var(--muted);
  opacity: 0;
}
.false-rule::after { content: ""; position: absolute; left: 12%; right: 12%; top: 50%; height: 3px; background: var(--red); transform: rotate(-5deg) scaleX(0); transform-origin: left; transition: transform .7s var(--ease); }
.trap-stage.cue--cross-false-rule .false-rule,
.trap-stage.cue--show-rule-boundary .false-rule { opacity: 1; }
.trap-stage.cue--cross-false-rule .false-rule::after,
.trap-stage.cue--show-rule-boundary .false-rule::after { transform: rotate(-5deg) scaleX(1); }

.memory-map { display: flex; justify-content: center; align-items: center; gap: 12px; opacity: 0; transform: translateY(8px); transition: opacity .4s, transform .6s var(--ease); }
.memory-map b { color: var(--coral); font-size: 25px; }
.memory-map i { color: var(--blue); font-style: normal; }
.trap-stage.cue--cross-false-rule .memory-map,
.trap-stage.cue--show-rule-boundary .memory-map { opacity: 1; transform: none; }

.rule-boundary { display: flex; flex-wrap: wrap; justify-content: center; gap: 8px; opacity: 0; transform: translateY(8px); transition: opacity .4s, transform .6s var(--ease); }
.rule-boundary > .boundary-condition {
  min-height: 46px;
  display: grid;
  align-content: center;
  gap: 2px;
  padding: 7px 11px;
  border-radius: 12px;
  background: var(--surface-soft);
  color: var(--ink);
}
.boundary-condition small { color: var(--muted); font-size: 11px; font-weight: 650; line-height: 1.15; }
.boundary-condition strong { font-size: 14px; font-weight: 720; line-height: 1.2; white-space: nowrap; }
.boundary-condition .katex { font-size: 1em; }
.trap-stage.cue--show-rule-boundary .rule-boundary { opacity: 1; transform: none; }

.transfer-map { display: flex; justify-content: center; gap: 14px; }
.transfer-map > span { min-width: 116px; min-height: 58px; display: flex; justify-content: center; align-items: center; gap: 12px; border-radius: 14px; background: var(--surface); opacity: 0; transform: scale(.92); transition: opacity .4s, transform .6s var(--ease); }
.transfer-map b { color: var(--coral); font-size: 26px; }
.transfer-map i { color: var(--blue); font-style: normal; }
.transfer-stage.cue--show-transfer-map .transfer-map > span,
.transfer-stage.cue--unlock-transfer .transfer-map > span { opacity: 1; transform: none; }

.transfer-card { margin-top: 6px; }
.transfer-meta { display: flex; justify-content: space-between; align-items: center; margin-bottom: 18px; color: var(--muted); font-size: 13px; }
.transfer-meta strong { font-variant-numeric: tabular-nums; }
.transfer-prompt { min-height: 78px; display: grid; place-items: center; margin-bottom: 18px; font-size: 26px; text-align: center; }
.why-copy { padding: 12px 0 0; color: var(--muted); font-size: 15px; }
.why-copy .feedback-math { color: var(--ink); }

.lesson-result { text-align: center; }
.result-mark { width: 64px; height: 64px; margin: 0 auto 16px; display: grid; place-items: center; border-radius: 50%; background: var(--green); color: #00180a; font-size: 36px; font-weight: 800; }
.lesson-result h3 { margin-bottom: 10px; }
.lesson-result p { color: var(--muted); }
.result-equations { display: grid; gap: 10px; margin: 22px 0; padding: 18px 0; border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); font-size: 18px; }

.page-nav {
  position: absolute;
  z-index: 20;
  left: 0;
  right: 0;
  bottom: 0;
  height: calc(var(--nav-height) + env(safe-area-inset-bottom));
  padding: 7px 14px max(7px, env(safe-area-inset-bottom));
  display: flex;
  align-items: center;
  justify-content: space-between;
  background: rgba(0, 0, 0, .94);
  border-top: 1px solid rgba(255, 255, 255, .1);
  backdrop-filter: saturate(145%) blur(18px);
}

.page-arrows { display: flex; gap: 6px; }
.page-arrow { width: 44px; height: 44px; border: 0; border-radius: 50%; background: var(--surface-soft); cursor: pointer; }
.page-arrow:disabled { opacity: .3; cursor: default; }
.page-nav p { margin: 0; padding: 4px 10px; color: var(--muted); font-size: 13px; font-variant-numeric: tabular-nums; }
.page-nav p i { padding: 0 3px; font-style: normal; opacity: .5; }

dialog {
  width: min(calc(100% - 28px), 402px);
  max-height: 72dvh;
  padding: 20px;
  border: 0;
  border-radius: 16px;
  background: #1c1c1e;
  color: var(--ink);
}
dialog::backdrop { background: rgba(0, 0, 0, .7); backdrop-filter: blur(4px); }
.dialog-head { display: flex; align-items: flex-start; justify-content: space-between; gap: 14px; }
.dialog-head h2 { font-size: 24px; }
.dialog-head button { width: 44px; height: 44px; border: 0; border-radius: 50%; background: var(--surface-soft); cursor: pointer; }
#transcript-copy { color: var(--muted); }

.lesson.is-review {
  height: auto;
  min-height: 100dvh;
  overflow: visible;
  padding-bottom: 40px;
}
.lesson.is-review .lesson-page {
  position: relative;
  inset: auto;
  min-height: auto;
  overflow: visible;
  border-bottom: 1px solid var(--line);
  pointer-events: auto;
}
.lesson.is-review .lesson-page[hidden] { display: block !important; }
.lesson.is-review .page-scroll { height: auto; min-height: 100dvh; overflow: visible; padding-top: 72px; }
.app-shell.is-review { overflow: visible; }
.app-shell.is-review .player { position: sticky; }

@media (max-width: 370px) {
  :root { --page-gap: 16px; }
  .text-button { display: none; }
  .hero-log { font-size: 48px; }
  .hero-power { font-size: 24px; }
  .machine-pair { flex-direction: column; }
  .mini-machine { min-height: 64px; }
  .trap-comparison { grid-template-columns: 1fr; }
  .comparison-sign { min-height: 26px; }
  .transfer-map > span { min-width: 104px; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; animation-duration: .01ms !important; animation-iteration-count: 1 !important; transition-duration: .01ms !important; }
}