:root {
  color-scheme: light;
  --paper: #f5f0e5;
  --paper-deep: #e8dfcf;
  --ink: #24362f;
  --ink-soft: #5d6c66;
  --line: #887d6c;
  --coral: #d86648;
  --coral-dark: #a9432c;
  --sage: #8da98f;
  --sage-pale: #dbe5d8;
  --mustard: #d7a33a;
  --white: #fffdf8;
  --shadow: 0 18px 50px rgb(48 53 44 / 10%);
  font-family:
    "PingFang SC", "Microsoft YaHei", "Noto Sans CJK SC", system-ui, sans-serif;
  font-synthesis: none;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-width: 320px;
  min-height: 100vh;
  color: var(--ink);
  background:
    radial-gradient(circle at 15% 10%, rgb(255 255 255 / 70%), transparent 24rem),
    linear-gradient(110deg, transparent 0 49%, rgb(85 91 72 / 3%) 49% 51%, transparent 51%),
    var(--paper);
}

button,
textarea,
input,
select {
  font: inherit;
}

button {
  color: inherit;
}

button:focus-visible,
a:focus-visible,
textarea:focus-visible,
input:focus-visible,
select:focus-visible {
  outline: 3px solid var(--coral-dark);
  outline-offset: 3px;
}

.skip-link {
  position: fixed;
  top: 8px;
  left: 8px;
  z-index: 20;
  min-height: 44px;
  padding: 11px 15px;
  color: var(--white);
  background: var(--ink);
  transform: translateY(-160%);
  transition: transform 180ms ease;
}

.skip-link:focus-visible {
  transform: translateY(0);
}

.app-shell {
  display: grid;
  grid-template:
    "topbar topbar" 76px
    "rail main" calc(100vh - 76px)
    / 310px minmax(0, 1fr);
}

.topbar {
  grid-area: topbar;
  display: grid;
  grid-template-columns: 310px 1fr auto;
  align-items: center;
  border-bottom: 1px solid var(--line);
  background: rgb(255 253 248 / 72%);
  backdrop-filter: blur(16px);
  position: relative;
  z-index: 3;
}

.brand {
  display: flex;
  align-items: center;
  gap: 12px;
  height: 100%;
  padding: 0 30px;
  color: inherit;
  text-decoration: none;
  border-right: 1px solid var(--line);
  transition:
    background 180ms ease,
    box-shadow 180ms ease;
}

.brand:hover {
  background: var(--paper-deep);
}

.brand:active {
  box-shadow: inset 0 -3px 0 var(--coral-dark);
}

.brand-mark {
  display: grid;
  place-items: center;
  width: 42px;
  aspect-ratio: 1;
  background: var(--ink);
  color: var(--paper);
  font-family: "STKaiti", "KaiTi", serif;
  font-size: 18px;
  transform: rotate(-2deg);
}

.brand-name {
  font-weight: 750;
  letter-spacing: 0.08em;
}

.term-label {
  display: flex;
  align-items: baseline;
  gap: 10px;
  padding: 0 30px;
  font-size: 13px;
  color: var(--ink-soft);
}

.term-label strong {
  color: var(--ink);
  font-size: 14px;
}

.map-button,
.primary-button,
.secondary-button,
.choice-button,
.round-button {
  border: 0;
  cursor: pointer;
  transition:
    background 180ms ease,
    color 180ms ease,
    box-shadow 180ms ease,
    transform 180ms ease;
}

.map-button {
  min-height: 44px;
  margin-right: 24px;
  padding: 11px 16px;
  border: 1px solid var(--ink);
  background: transparent;
  font-weight: 700;
}

.map-button:active,
.icon-button:active {
  transform: scale(0.98);
}

.secondary-button:active {
  background: var(--paper-deep);
  transform: scale(0.98);
}

.map-button span {
  display: inline-block;
  margin-right: 7px;
  color: var(--coral);
}

.map-button:hover,
.secondary-button:hover,
.icon-button:hover {
  background: var(--ink);
  color: var(--white);
}

.route-rail {
  grid-area: rail;
  overflow: auto;
  padding: 34px 30px;
  border-right: 1px solid var(--line);
  background: rgb(232 223 207 / 48%);
}

.eyebrow {
  margin: 0 0 9px;
  color: var(--coral-dark);
  font-size: 12px;
  font-weight: 800;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.route-rail h2 {
  margin: 0;
  font-family: "STKaiti", "KaiTi", serif;
  font-size: 25px;
  line-height: 1.35;
  font-weight: 700;
}

.route-list {
  list-style: none;
  margin: 34px 0;
  padding: 0;
  position: relative;
}

.route-list::before {
  content: "";
  position: absolute;
  top: 13px;
  bottom: 17px;
  left: 13px;
  width: 1px;
  background: var(--line);
}

.route-list li {
  display: grid;
  grid-template-columns: 28px 1fr;
  gap: 13px;
  align-items: start;
  position: relative;
  padding: 0 0 25px;
  color: var(--ink-soft);
  font-size: 14px;
  line-height: 1.4;
}

.route-list a {
  color: inherit;
  text-decoration-color: var(--coral);
  text-underline-offset: 3px;
}

.route-list a:hover {
  color: var(--coral-dark);
}

.money-summary {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
  margin: 22px 0;
  padding: 20px;
  border: 1px solid var(--line);
  background: var(--white);
}

.ten-note,
.one-coin {
  display: inline-grid;
  place-items: center;
  font-weight: 800;
}

.ten-note {
  width: 72px;
  height: 38px;
  border: 2px solid var(--sage);
  background: var(--sage-pale);
}

.one-coin {
  width: 38px;
  aspect-ratio: 1;
  border: 2px solid var(--mustard);
  border-radius: 50%;
  background: #f6e6b7;
}

.path-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin: 24px 0 16px;
}

.path-tabs .active {
  color: var(--white);
  background: var(--ink);
}

.money-lab {
  display: grid;
  gap: 18px;
  padding: 24px;
  border: 1px solid var(--line);
  background: var(--white);
}

.money-pool {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
  padding-bottom: 14px;
  border-bottom: 1px dashed var(--line);
}

.money-pool small {
  color: var(--ink-soft);
}

.money-children {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 12px;
}

.money-children div {
  display: grid;
  place-items: center;
  gap: 5px;
  min-height: 112px;
  padding: 12px;
  background: var(--sage-pale);
}

.money-children span {
  font-size: 28px;
}

.money-children em {
  color: var(--coral-dark);
  font-size: 18px;
  font-style: normal;
  font-weight: 800;
}

.path-comparison {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin: 20px 0;
}

.path-comparison div {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  padding: 16px;
  border: 1px solid var(--line);
}

.path-comparison strong {
  color: var(--coral-dark);
  font-size: 24px;
}

.path-comparison p {
  grid-column: 1 / -1;
  margin: 0;
  padding: 14px 16px;
  background: var(--sage-pale);
}

.practice-skill {
  color: var(--coral-dark);
  font-weight: 750;
}

.hint-card {
  margin-top: 12px;
  padding: 14px 16px;
  border-left: 4px solid var(--mustard);
  background: #fff7df;
}

.hint-card p {
  margin: 5px 0 0;
}

.link-button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  text-decoration: none;
}

@media (max-width: 680px) {
  .money-children,
  .path-comparison {
    grid-template-columns: 1fr;
  }

  .path-comparison p {
    grid-column: auto;
  }
}

.route-list small {
  display: block;
  margin-bottom: 3px;
  color: var(--ink-soft);
  font-size: 11px;
}

.route-dot {
  display: grid;
  place-items: center;
  width: 28px;
  height: 28px;
  border: 1px solid var(--line);
  background: var(--paper);
  font-size: 12px;
  font-weight: 800;
  z-index: 1;
}

.route-done .route-dot {
  border-color: var(--sage);
  background: var(--sage-pale);
  color: #46664d;
}

.route-current {
  color: var(--ink) !important;
  font-weight: 750;
}

.route-current .route-dot {
  border-color: var(--coral);
  background: var(--coral-dark);
  color: white;
  box-shadow: 0 0 0 5px rgb(216 102 72 / 13%);
}

.route-review-banner {
  display: grid;
  gap: 8px;
  margin: -8px 0 24px;
  padding: 16px;
  border: 1px solid var(--mustard);
  background: #fff7de;
  font-size: 13px;
  line-height: 1.5;
}

.route-review-banner[hidden] {
  display: none;
}

.route-review-banner span {
  color: var(--ink-soft);
}

.route-review-banner button {
  min-height: 44px;
  margin-top: 3px;
  border: 1px solid var(--ink);
  background: var(--ink);
  color: var(--white);
  cursor: pointer;
  font-weight: 800;
  transition:
    background 180ms ease,
    transform 180ms ease;
}

.route-review-banner button:hover {
  background: #17261f;
  transform: translateY(-1px);
}

.route-review-banner button:active {
  transform: scale(0.98);
}

.parent-note {
  border-top: 1px solid var(--line);
  padding-top: 18px;
  font-size: 13px;
  line-height: 1.65;
}

.parent-note span {
  color: var(--coral-dark);
  font-weight: 800;
}

.parent-note p {
  margin: 7px 0 0;
  color: var(--ink-soft);
}

.lesson-main {
  grid-area: main;
  overflow: auto;
  padding: 26px clamp(24px, 5vw, 72px) 60px;
}

.lesson-progress {
  display: grid;
  grid-template-columns: auto minmax(120px, 1fr) auto;
  align-items: center;
  gap: 16px;
  max-width: 1040px;
  margin: 0 auto 22px;
  color: var(--ink-soft);
  font-size: 12px;
  font-weight: 700;
}

.progress-track {
  height: 5px;
  overflow: hidden;
  background: var(--paper-deep);
}

.progress-track span {
  display: block;
  width: 0;
  height: 100%;
  background: linear-gradient(90deg, var(--coral), var(--mustard));
  transition: width 350ms ease;
}

.lesson-screen {
  max-width: 1040px;
  min-height: 640px;
  margin: 0 auto;
}

.lesson-card {
  min-height: 620px;
  padding: clamp(28px, 5vw, 62px);
  border: 1px solid var(--line);
  background:
    linear-gradient(90deg, rgb(83 104 82 / 4%) 1px, transparent 1px) 0 0 / 32px 32px,
    linear-gradient(rgb(83 104 82 / 4%) 1px, transparent 1px) 0 0 / 32px 32px,
    var(--white);
  box-shadow: var(--shadow);
  position: relative;
}

.lesson-card::after {
  content: "";
  position: absolute;
  top: -9px;
  right: 8%;
  width: 110px;
  height: 23px;
  background: rgb(215 163 58 / 28%);
  transform: rotate(2deg);
}

.lesson-kicker {
  display: flex;
  align-items: center;
  gap: 9px;
  margin-bottom: 22px;
  color: var(--coral-dark);
  font-size: 13px;
  font-weight: 800;
}

.lesson-kicker::before {
  content: "";
  width: 30px;
  height: 2px;
  background: var(--coral);
}

.lesson-card h1,
.lesson-card h2 {
  max-width: 760px;
  margin: 0;
  font-family: "STKaiti", "KaiTi", serif;
  font-weight: 700;
  letter-spacing: -0.02em;
}

.lesson-card h1,
.lesson-card .lesson-title {
  font-size: clamp(38px, 5.4vw, 68px);
  line-height: 1.08;
}

.lesson-card h2 {
  font-size: clamp(32px, 4vw, 50px);
  line-height: 1.15;
}

.lead {
  max-width: 700px;
  margin: 24px 0;
  color: var(--ink-soft);
  font-size: clamp(16px, 1.8vw, 20px);
  line-height: 1.8;
}

.origin-line {
  display: grid;
  grid-template-columns: 74px 1fr;
  gap: 16px;
  max-width: 710px;
  margin: 30px 0;
  padding: 19px 0;
  border-block: 1px solid var(--line);
}

.origin-line strong {
  color: var(--coral-dark);
  font-size: 13px;
}

.origin-line p {
  margin: 0;
  line-height: 1.65;
}

.meta-row {
  display: flex;
  flex-wrap: wrap;
  gap: 10px 24px;
  margin: 26px 0 36px;
  color: var(--ink-soft);
  font-size: 13px;
}

.meta-row span::before {
  content: "·";
  margin-right: 8px;
  color: var(--coral);
}

.primary-button,
.secondary-button {
  min-height: 48px;
  padding: 13px 22px;
  font-weight: 800;
}

.primary-button {
  background: var(--ink);
  color: var(--white);
  box-shadow: 5px 5px 0 var(--mustard);
}

.primary-button:hover {
  background: #17261f;
  transform: translateY(-1px);
}

.primary-button:active {
  box-shadow: 2px 2px 0 var(--mustard);
  transform: translate(3px, 3px);
}

.secondary-button {
  border: 1px solid var(--ink);
  background: transparent;
}

.button-row {
  display: flex;
  flex-wrap: wrap;
  gap: 14px;
  align-items: center;
  margin-top: 30px;
}

.question-sheet {
  margin-top: 28px;
  padding: 28px;
  border-left: 5px solid var(--mustard);
  background: #fbf6e8;
}

.big-equation {
  margin: 0 0 10px;
  font-family: ui-monospace, "SFMono-Regular", monospace;
  font-size: clamp(28px, 5vw, 48px);
  letter-spacing: 0.04em;
}

.choice-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
  max-width: 760px;
  margin-top: 25px;
}

.choice-button {
  min-height: 72px;
  padding: 17px 20px;
  border: 1px solid var(--line);
  background: var(--white);
  text-align: left;
  font-weight: 750;
}

.choice-button:hover {
  border-color: var(--coral);
  background: #fff8ef;
}

.choice-button:active {
  border-color: var(--coral-dark);
  background: #fbe5d8;
}

.video-layout {
  display: grid;
  grid-template-columns: minmax(250px, 390px) minmax(280px, 1fr);
  gap: clamp(26px, 5vw, 64px);
  align-items: center;
  margin-top: 30px;
}

.video-frame {
  padding: 12px;
  background: #17201c;
  box-shadow: 9px 9px 0 var(--sage);
}

.video-frame video {
  display: block;
  width: 100%;
  max-height: 560px;
  aspect-ratio: 9 / 16;
  object-fit: contain;
  background: black;
}

.source-line {
  margin-top: 15px;
  color: var(--ink-soft);
  font-size: 12px;
  line-height: 1.6;
}

.source-line a {
  display: inline-block;
  min-height: 44px;
  padding-block: 13px;
  color: var(--coral-dark);
  transition:
    background 180ms ease,
    color 180ms ease;
}

.source-line a:hover {
  background: var(--paper-deep);
}

.source-line a:active {
  color: var(--ink);
}

.watch-list {
  margin: 25px 0 0;
  padding: 0;
  list-style: none;
}

.watch-list li {
  display: grid;
  grid-template-columns: 26px 1fr;
  gap: 10px;
  margin: 13px 0;
  line-height: 1.55;
}

.watch-list li::before {
  content: "→";
  color: var(--coral);
  font-weight: 900;
}

.sharing-layout {
  display: grid;
  grid-template-columns: 1fr 250px;
  gap: 34px;
  align-items: start;
  margin-top: 30px;
}

.children {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 15px;
}

.child {
  min-height: 190px;
  padding: 20px 12px;
  border-bottom: 4px solid var(--sage);
  background: var(--sage-pale);
  text-align: center;
}

.child-face {
  display: grid;
  place-items: center;
  width: 52px;
  height: 52px;
  margin: 0 auto 15px;
  border: 2px solid var(--ink);
  border-radius: 50%;
  font-size: 24px;
}

.child strong {
  display: block;
  margin-bottom: 13px;
}

.child-candies,
.candy-pile {
  min-height: 32px;
  color: var(--coral);
  font-size: 23px;
  letter-spacing: 3px;
}

.candy-box {
  padding: 22px;
  border: 2px dashed var(--mustard);
  background: #fff8e9;
  text-align: center;
}

.candy-box strong {
  display: block;
  margin-bottom: 8px;
}

.round-button {
  width: 100%;
  margin-top: 16px;
  padding: 13px;
  background: var(--coral-dark);
  color: white;
  font-weight: 800;
}

.round-button:disabled {
  cursor: not-allowed;
  opacity: 0.45;
}

.round-button:not(:disabled):hover {
  background: #7f2f20;
}

.round-button:not(:disabled):active {
  transform: scale(0.98);
}

.sharing-next-reason {
  margin: 12px 0 0;
  color: var(--ink-soft);
  font-size: 13px;
  line-height: 1.55;
  text-align: left;
}

.equation-strip {
  margin-top: 24px;
  padding: 17px 20px;
  border-left: 4px solid var(--coral);
  background: var(--paper);
  font-family: ui-monospace, "SFMono-Regular", monospace;
  font-size: clamp(18px, 2.8vw, 28px);
}

.feedback {
  max-width: 760px;
  margin-top: 22px;
  padding: 16px 18px;
  border: 1px solid;
  line-height: 1.65;
}

.feedback.intermediate {
  border-color: var(--mustard);
  background: #fff7de;
}

.feedback.success {
  border-color: var(--sage);
  background: #edf5eb;
}

.feedback.error {
  border-color: var(--coral);
  background: #fff0eb;
}

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

.practice-card {
  overflow-wrap: anywhere;
}

.practice-card h2 {
  max-width: 820px;
  font-size: clamp(29px, 3.8vw, 46px);
  line-height: 1.28;
}

.skill-label {
  display: inline-block;
  margin: 0 0 15px;
  padding: 7px 11px;
  border-left: 3px solid var(--sage);
  color: var(--ink);
  background: var(--sage-pale);
  font-size: 13px;
  font-weight: 800;
}

#practice-form {
  max-width: 820px;
  margin-top: 30px;
}

.practice-options {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 13px;
  min-width: 0;
  margin: 0;
  padding: 0;
  border: 0;
}

.practice-option {
  display: grid;
  grid-template-columns: 24px minmax(0, 1fr);
  gap: 12px;
  align-items: center;
  min-height: 64px;
  padding: 13px 15px;
  border: 2px solid var(--line);
  background: var(--white);
  cursor: pointer;
  transition:
    background 180ms ease,
    border-color 180ms ease,
    box-shadow 180ms ease,
    transform 180ms ease;
}

.practice-option input {
  width: 20px;
  height: 20px;
  margin: 0;
  accent-color: var(--coral-dark);
}

.practice-option span {
  min-width: 0;
  line-height: 1.45;
}

.practice-option:hover {
  border-color: var(--coral);
  background: #fff8ef;
  transform: translateY(-1px);
}

.practice-option:active {
  border-color: var(--coral-dark);
  background: #fbe5d8;
  transform: scale(0.99);
}

.practice-option:has(input:checked) {
  border-color: var(--coral-dark);
  background: #fff0e8;
  box-shadow: inset 5px 0 0 var(--coral);
}

.practice-option:has(input:focus-visible) {
  outline: 3px solid var(--coral-dark);
  outline-offset: 3px;
}

.practice-option input:focus-visible {
  outline: 0;
}

.numeric-answer {
  display: grid;
  gap: 8px;
  max-width: 300px;
  font-weight: 800;
}

.numeric-answer input {
  width: 100%;
  min-height: 52px;
  padding: 9px 13px;
  border: 2px solid var(--line);
  border-radius: 0;
  color: var(--ink);
  background: var(--white);
  font-size: 22px;
  transition:
    background 180ms ease,
    border-color 180ms ease;
}

.numeric-answer input:hover {
  border-color: var(--coral);
  background: #fffdf9;
}

.practice-options[aria-invalid="true"],
.numeric-answer input[aria-invalid="true"] {
  border-color: var(--coral-dark);
}

.hint-panel {
  max-width: 720px;
  margin-top: 20px;
  padding: 14px 17px;
  border-left: 4px solid var(--mustard);
  color: var(--ink-soft);
  background: #fff8e9;
  line-height: 1.6;
}

.hint-panel strong {
  color: var(--ink);
}

.hint-panel p,
.practice-feedback p,
.diagnostic-notice p,
.practice-completion p {
  margin: 4px 0 0;
}

.practice-feedback strong {
  display: block;
}

.practice-feedback.success strong::before {
  content: "✓ ";
}

.practice-feedback.error strong::before {
  content: "! ";
}

.diagnostic-notice {
  max-width: 820px;
  margin: 22px 0 0;
  padding: 14px 17px;
  border: 1px dashed var(--sage);
  background: rgb(219 229 216 / 58%);
  line-height: 1.6;
}

.diagnostic-notice strong::before {
  content: "＋ ";
  color: var(--coral-dark);
}

.practice-card button {
  transition:
    background 180ms ease,
    color 180ms ease,
    box-shadow 180ms ease,
    transform 180ms ease;
}

.practice-card .secondary-button:active {
  background: var(--paper-deep);
  transform: scale(0.98);
}

.practice-card button:disabled,
.practice-card button:disabled:hover,
.practice-card button:disabled:active {
  cursor: not-allowed;
  opacity: 0.58;
  color: var(--ink-soft);
  background: var(--paper-deep);
  box-shadow: none;
  transform: none;
}

.practice-card button:focus-visible,
.practice-card input:focus-visible {
  outline-color: var(--coral-dark);
}

.practice-completion {
  margin-bottom: 28px;
}

.formula-card {
  max-width: 760px;
  margin: 28px 0;
  padding: 25px;
  border: 1px solid var(--ink);
  background: var(--white);
}

.formula-card .formula {
  font-family: ui-monospace, "SFMono-Regular", monospace;
  font-size: clamp(25px, 4vw, 40px);
}

.formula-card p {
  margin: 13px 0 0;
  color: var(--ink-soft);
  line-height: 1.65;
}

.week-row {
  display: grid;
  grid-template-columns: repeat(7, minmax(42px, 1fr));
  gap: 7px;
  max-width: 760px;
  margin: 28px 0;
}

.week-row span {
  display: grid;
  place-items: center;
  min-height: 58px;
  border: 1px solid var(--line);
  background: var(--white);
  font-weight: 750;
}

.week-row span:last-child {
  border-color: var(--coral);
  color: var(--coral-dark);
}

.summary-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1px;
  max-width: 800px;
  margin: 30px 0;
  background: var(--line);
  border: 1px solid var(--line);
}

.summary-grid article {
  padding: 22px;
  background: var(--white);
}

.summary-grid small {
  color: var(--coral-dark);
  font-weight: 800;
}

.summary-grid h3 {
  margin: 8px 0 7px;
  font-family: "STKaiti", "KaiTi", serif;
  font-size: 24px;
}

.summary-grid p {
  margin: 0;
  color: var(--ink-soft);
  line-height: 1.6;
}

.explain-box {
  max-width: 800px;
  margin-top: 25px;
}

.explain-box label {
  display: block;
  margin-bottom: 9px;
  font-weight: 800;
}

.explain-box textarea {
  width: 100%;
  min-height: 92px;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 0;
  resize: vertical;
  color: var(--ink);
  background: var(--white);
  transition:
    background 180ms ease,
    border-color 180ms ease;
}

.explain-box textarea:hover {
  border-color: var(--coral-dark);
  background: #fffdf9;
}

.concept-map {
  width: min(1180px, calc(100vw - 32px));
  height: min(880px, calc(100vh - 32px));
  max-height: calc(100vh - 32px);
  padding: 0;
  border: 1px solid var(--ink);
  color: var(--ink);
  background: var(--paper);
  box-shadow: 0 30px 90px rgb(20 29 25 / 28%);
  overflow: auto;
}

.concept-map::backdrop {
  background: rgb(29 38 34 / 58%);
  backdrop-filter: blur(4px);
}

.map-header {
  display: flex;
  align-items: start;
  justify-content: space-between;
  gap: 20px;
  padding: 28px 32px 18px;
  border-bottom: 1px solid var(--line);
}

.map-header h2 {
  margin: 0;
  font-family: "STKaiti", "KaiTi", serif;
  font-size: clamp(25px, 4vw, 38px);
}

.icon-button {
  flex: 0 0 auto;
  width: 44px;
  height: 44px;
  border: 1px solid var(--ink);
  background: transparent;
  cursor: pointer;
  font-size: 24px;
  transition:
    background 180ms ease,
    color 180ms ease,
    transform 180ms ease;
}

.map-toolbar {
  display: grid;
  grid-template-columns: minmax(220px, 1.3fr) repeat(2, minmax(180px, 1fr));
  gap: 14px;
  padding: 18px 24px;
  border-bottom: 1px solid var(--line);
  background:
    linear-gradient(90deg, rgb(83 104 82 / 4%) 1px, transparent 1px) 0 0 / 24px 24px,
    var(--white);
}

.map-toolbar label {
  display: grid;
  gap: 6px;
  color: var(--ink-soft);
  font-size: 12px;
  font-weight: 800;
}

.map-toolbar input,
.map-toolbar select {
  width: 100%;
  min-height: 44px;
  padding: 9px 12px;
  border: 1px solid var(--line);
  border-radius: 0;
  color: var(--ink);
  background: var(--white);
  transition:
    background 180ms ease,
    border-color 180ms ease;
}

.map-toolbar input:hover,
.map-toolbar select:hover {
  border-color: var(--sage);
}

.map-toolbar input:focus-visible,
.map-toolbar select:focus-visible {
  border-color: var(--coral-dark);
}

.full-map-layout {
  display: grid;
  grid-template-columns: minmax(0, 2fr) minmax(280px, 0.9fr);
  align-items: start;
}

.map-overview {
  min-width: 0;
  padding: 24px;
  border-right: 1px solid var(--line);
}

.map-results {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: 6px;
  margin-bottom: 22px;
  color: var(--ink-soft);
  font-size: 13px;
}

.map-results strong {
  color: var(--coral-dark);
  font-family: "STKaiti", "KaiTi", serif;
  font-size: 26px;
}

.map-results span {
  flex-basis: 100%;
}

.map-band-group + .map-band-group {
  margin-top: 30px;
  padding-top: 26px;
  border-top: 1px dashed var(--line);
}

.map-band-group > header {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px 10px;
  margin-bottom: 13px;
}

.map-band-group h3 {
  margin: 0 auto 0 0;
  font-family: "STKaiti", "KaiTi", serif;
  font-size: 23px;
}

.map-band-group > header > span:last-child {
  color: var(--ink-soft);
  font-size: 12px;
}

.route-badge {
  padding: 3px 7px;
  border: 1px solid var(--sage);
  background: var(--sage-pale);
  color: #46664d;
  font-size: 10px;
  font-weight: 800;
  letter-spacing: 0.04em;
}

.route-badge--bridge {
  border-style: dashed;
  border-color: var(--mustard);
  background: #fff7de;
  color: #805f1d;
}

.map-node-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 10px;
}

.map-node-button {
  min-width: 0;
  min-height: 86px;
  padding: 13px 12px;
  border: 1px solid var(--line);
  background: var(--white);
  cursor: pointer;
  position: relative;
  text-align: left;
  transition:
    background 180ms ease,
    border-color 180ms ease,
    box-shadow 180ms ease,
    transform 180ms ease;
}

.map-node-button--available {
  border: 2px solid var(--sage);
  background: #f5faf3;
}

.map-node-button--map-only {
  border-style: dashed;
  background:
    linear-gradient(135deg, transparent 0 88%, rgb(141 169 143 / 20%) 88%),
    var(--white);
}

.map-node-button--current {
  border-left: 6px solid var(--coral);
  background: #fff5eb;
}

.map-node-button:hover {
  border-color: var(--coral);
  background: #fff9f2;
  box-shadow: 3px 3px 0 var(--paper-deep);
  transform: translateY(-2px);
}

.map-node-button:active {
  box-shadow: 1px 1px 0 var(--paper-deep);
  transform: translate(1px, 1px);
}

.map-node-button[aria-pressed="true"] {
  box-shadow:
    inset 0 0 0 2px var(--ink),
    4px 4px 0 var(--mustard);
}

.map-node-button[aria-pressed="true"]::after {
  content: "✓ 已选";
  display: block;
  margin-top: 8px;
  color: var(--coral-dark);
  font-size: 10px;
  font-weight: 900;
}

.map-node-title {
  display: block;
  overflow-wrap: anywhere;
  font-family: "STKaiti", "KaiTi", serif;
  font-size: 17px;
  font-weight: 750;
  line-height: 1.35;
}

.map-node-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 5px;
  margin-top: 9px;
  color: var(--ink-soft);
  font-size: 10px;
  font-weight: 750;
}

.map-node-meta em {
  padding: 1px 5px;
  background: var(--coral-dark);
  color: white;
  font-style: normal;
}

.map-detail {
  position: sticky;
  top: 0;
  min-width: 0;
  max-height: calc(100vh - 34px);
  padding: 26px 24px 40px;
  overflow: auto;
  background: rgb(255 253 248 / 86%);
}

.detail-heading p {
  margin: 0 0 8px;
  color: var(--coral-dark);
  font-size: 11px;
  font-weight: 850;
}

.detail-heading h2 {
  margin: 0;
  overflow-wrap: anywhere;
  font-family: "STKaiti", "KaiTi", serif;
  font-size: clamp(25px, 3vw, 34px);
  line-height: 1.2;
}

.detail-heading h2:focus-visible {
  outline: 3px solid var(--coral-dark);
  outline-offset: 4px;
}

.map-return-button {
  display: block;
  min-height: 44px;
  margin-top: 14px;
  padding: 9px 12px;
  border: 1px solid var(--ink);
  background: transparent;
  cursor: pointer;
  font-size: 12px;
  font-weight: 800;
  transition:
    background 180ms ease,
    color 180ms ease,
    transform 180ms ease;
}

.map-return-button:hover {
  background: var(--ink);
  color: var(--white);
  transform: translateX(-2px);
}

.map-return-button:active {
  transform: translateX(-2px) scale(0.98);
}

.detail-status {
  display: inline-block;
  margin-top: 12px;
  padding: 5px 8px;
  border: 1px solid var(--sage);
  background: var(--sage-pale);
  font-size: 11px;
  font-weight: 850;
}

.detail-status--map-only {
  border-style: dashed;
  border-color: var(--line);
  background: var(--paper);
}

.detail-summary,
.detail-why p,
.detail-recommendation,
.relation-group p,
.foundation-paths > p {
  color: var(--ink-soft);
  font-size: 13px;
  line-height: 1.65;
}

.detail-summary {
  margin: 18px 0;
  font-size: 15px;
}

.detail-why,
.detail-recommendation {
  padding: 14px;
  border-left: 3px solid var(--coral);
  background: #fff5eb;
}

.detail-why h3,
.relation-group h3,
.foundation-paths h3 {
  margin: 0 0 7px;
  font-size: 13px;
}

.detail-why p,
.detail-recommendation,
.relation-group p,
.foundation-paths > p {
  margin-block: 0;
}

.detail-recommendation {
  margin: 10px 0 22px;
  border-left-color: var(--sage);
  background: var(--sage-pale);
}

.relation-group,
.foundation-paths {
  margin-top: 20px;
  padding-top: 17px;
  border-top: 1px solid var(--line);
}

.relation-links {
  display: grid;
  gap: 7px;
}

.relation-links button {
  min-height: 44px;
  padding: 8px 10px;
  border: 1px solid var(--line);
  background: var(--white);
  cursor: pointer;
  overflow-wrap: anywhere;
  text-align: left;
  transition:
    background 180ms ease,
    border-color 180ms ease,
    transform 180ms ease;
}

.relation-links button:hover {
  border-color: var(--coral);
  background: #fff5eb;
  transform: translateX(2px);
}

.relation-links button:active {
  transform: translateX(2px) scale(0.98);
}

.foundation-path-list {
  display: grid;
  gap: 10px;
  margin-top: 12px;
  padding: 0;
  list-style: none;
}

.foundation-path {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 5px;
  padding: 10px;
  border: 1px dashed var(--sage);
  background: rgb(219 229 216 / 42%);
}

.foundation-path-node {
  padding: 3px 5px;
  border-bottom: 1px solid var(--sage);
  color: var(--ink);
  font-size: 11px;
}

.foundation-path > span[aria-hidden="true"] {
  color: var(--coral);
  font-weight: 900;
}

.map-empty {
  display: grid;
  gap: 8px;
  min-height: 180px;
  place-content: center;
  padding: 30px;
  border: 1px dashed var(--line);
  color: var(--ink-soft);
  text-align: center;
}

.map-empty strong {
  color: var(--ink);
  font-family: "STKaiti", "KaiTi", serif;
  font-size: 22px;
}

@media (max-width: 900px) {
  .app-shell {
    grid-template:
      "topbar" 70px
      "main" auto
      / 1fr;
  }

  .topbar {
    grid-template-columns: 1fr auto;
  }

  .brand {
    border-right: 0;
    padding-left: 18px;
  }

  .term-label,
  .route-rail {
    display: none;
  }

  .map-button {
    margin-right: 14px;
  }

  .lesson-main {
    padding: 20px 16px 40px;
  }

  .lesson-card {
    min-height: 0;
    padding: 30px 22px 38px;
  }

  .video-layout,
  .sharing-layout {
    grid-template-columns: 1fr;
  }

  .video-frame {
    max-width: 330px;
    margin: 0 auto;
  }
}

@media (max-width: 620px) {
  .brand-name,
  .progress-count {
    display: none;
  }

  .choice-grid,
  .summary-grid,
  .practice-options {
    grid-template-columns: 1fr;
  }

  .practice-card .button-row {
    align-items: stretch;
    flex-direction: column;
  }

  .practice-card .button-row button {
    width: 100%;
  }

  .children {
    gap: 7px;
  }

  .child {
    min-height: 150px;
    padding: 14px 6px;
  }

  .child-face {
    width: 42px;
    height: 42px;
    font-size: 19px;
  }

  .week-row {
    grid-template-columns: repeat(4, minmax(42px, 1fr));
  }

  .concept-map {
    width: calc(100vw - 16px);
    height: calc(100vh - 16px);
    max-height: calc(100vh - 16px);
  }

  .map-header {
    padding: 20px 16px 14px;
  }

  .map-header h2 {
    font-size: 25px;
  }

  .map-toolbar {
    grid-template-columns: 1fr;
    padding: 16px;
  }

  .full-map-layout {
    grid-template-columns: 1fr;
  }

  .map-overview {
    padding: 20px 16px 28px;
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .map-node-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }

  .map-node-button {
    min-height: 94px;
  }

  .map-detail {
    position: static;
    max-height: none;
    padding: 28px 16px 44px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    scroll-behavior: auto !important;
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
  }
}

.detail-lesson-link {
  display: grid;
  min-height: 44px;
  margin: 10px 0 22px;
  place-items: center;
  padding: 11px 14px;
  color: var(--white);
  background: var(--coral-dark);
  font-weight: 800;
  text-decoration: none;
  transition:
    background 180ms ease,
    transform 180ms ease;
}

.detail-lesson-link:hover {
  background: var(--ink);
}

.detail-lesson-link:active {
  transform: scale(0.98);
}

.hand-compare {
  display: grid;
  grid-template-columns: minmax(110px, 1fr) 2fr minmax(110px, 1fr);
  gap: 16px;
  align-items: end;
  margin: 28px 0;
}

.hand {
  display: grid;
  min-height: 90px;
  place-items: center;
  padding: 12px;
  border: 1px solid var(--ink);
  border-radius: 48% 48% 12px 12px;
  background: #f0c5a8;
  font-size: 13px;
  font-weight: 800;
  text-align: center;
}

.hand--child {
  min-height: 72px;
  transform: rotate(-4deg);
}

.hand--adult {
  transform: rotate(4deg);
}

.table-edge {
  display: block;
  height: 24px;
  border: 1px solid var(--ink);
  background:
    repeating-linear-gradient(
      90deg,
      #bc8352 0 30px,
      #c9915e 30px 60px
    );
  box-shadow: 0 8px 0 #765139;
}

.experiment-steps {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px;
  margin: 24px 0;
  padding: 0;
  list-style: none;
}

.experiment-steps li {
  display: grid;
  gap: 6px;
  padding: 16px;
  border: 1px solid var(--line);
  background: var(--white);
}

.experiment-steps strong {
  color: var(--coral-dark);
}

.experiment-steps span {
  color: var(--ink-soft);
  font-size: 13px;
  line-height: 1.55;
}

.measurement-form {
  margin: 22px 0;
  padding: 20px;
  border: 1px solid var(--line);
  background: rgb(255 253 248 / 70%);
}

.measurement-inputs {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
  margin-bottom: 16px;
}

.measurement-inputs label {
  display: grid;
  grid-template-columns: 1fr 90px auto;
  gap: 10px;
  align-items: center;
  padding: 12px;
  border: 1px solid var(--line);
  background: var(--white);
}

.measurement-inputs label > span {
  font-weight: 750;
}

.measurement-inputs input {
  width: 100%;
  min-height: 44px;
  border: 1px solid var(--ink);
  background: var(--paper);
  color: var(--ink);
  font-size: 20px;
  font-weight: 800;
  text-align: center;
  transition:
    background 180ms ease,
    border-color 180ms ease;
}

.measurement-inputs input:hover {
  border-color: var(--coral-dark);
  background: var(--white);
}

.measurement-inputs em {
  color: var(--ink-soft);
  font-style: normal;
}

.measure-result {
  margin: 18px 0;
}

.measure-result p {
  margin-bottom: 0;
}

.unit-strip-demo {
  display: grid;
  grid-template-columns: repeat(9, minmax(24px, 1fr));
  margin: 28px 0;
  border: 1px solid var(--ink);
  background: var(--white);
}

.unit-strip {
  display: grid;
  min-height: 84px;
  place-items: end center;
  padding: 7px 3px;
  border-right: 1px dashed var(--ink);
  background:
    linear-gradient(135deg, transparent 0 12px, rgb(215 163 58 / 24%) 12px 24px, transparent 24px);
}

.unit-strip:last-child {
  border-right: 0;
}

.unit-strip em {
  display: grid;
  width: 24px;
  height: 24px;
  place-items: center;
  border-radius: 50%;
  color: var(--white);
  background: var(--ink);
  font-size: 11px;
  font-style: normal;
}

@media (max-width: 620px) {
  .hand-compare {
    grid-template-columns: 74px 1fr 88px;
    gap: 8px;
  }

  .hand {
    min-height: 68px;
    padding: 7px;
    font-size: 11px;
  }

  .hand--child {
    min-height: 58px;
  }

  .experiment-steps,
  .measurement-inputs {
    grid-template-columns: 1fr;
  }

  .measurement-form {
    padding: 14px;
  }

  .measurement-inputs label {
    grid-template-columns: 1fr 82px auto;
  }

  .unit-strip {
    min-height: 64px;
  }
}

.experiment-paths {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1rem;
}

.partition-compare,
.fraction-strip,
.fraction-option-diagrams {
  display: grid;
  gap: 0.75rem;
}

.partition-compare,
.fraction-option-diagrams {
  grid-template-columns: repeat(2, minmax(0, 1fr));
  margin-block: 1.5rem;
}

.fraction-option-diagrams figure {
  min-width: 0;
  margin: 0;
}

.fraction-option-diagrams figcaption {
  margin-bottom: 0.5rem;
  font-weight: 800;
}

.fraction-strip {
  grid-template-columns: repeat(var(--fraction-parts), minmax(2.75rem, 1fr));
  gap: 0;
  border: 2px solid var(--ink);
  border-radius: 0.9rem;
  overflow: hidden;
  background: var(--paper);
}

.fraction-part {
  display: grid;
  min-height: 5rem;
  place-items: center;
  gap: 0.25rem;
  padding: 0.5rem;
  border: 0;
  border-inline-end: 1px solid var(--ink);
  background: var(--paper);
  color: var(--ink);
  text-align: center;
}

button.fraction-part {
  cursor: pointer;
  transition:
    background 180ms ease,
    box-shadow 180ms ease,
    transform 180ms ease;
}

button.fraction-part:hover {
  background: var(--sage-pale);
  transform: translateY(-1px);
}

button.fraction-part:active {
  box-shadow: inset 0 -0.25rem 0 var(--coral);
  transform: scale(0.98);
}

.fraction-part:last-child {
  border-inline-end: 0;
}

.fraction-part[aria-pressed="true"],
.fraction-part--selected {
  background: var(--sage-pale);
  box-shadow: inset 0 -0.45rem 0 var(--coral);
  font-weight: 800;
}

.experiment-paths .choice-button[aria-pressed="true"],
.partition-compare .choice-button[aria-pressed="true"],
.question-sheet .choice-button[aria-pressed="true"],
.fraction-experiment .secondary-button[aria-pressed="true"] {
  border-color: var(--coral-dark);
  background: var(--sage-pale);
  box-shadow: inset 0 -0.3rem 0 var(--coral);
}

.fraction-part:focus-visible,
.experiment-paths button:focus-visible {
  outline: 3px solid var(--coral-dark);
  outline-offset: 3px;
}

.partition-unequal {
  grid-template-columns: 2fr 4fr 3fr 3fr;
}

.visual-text {
  max-width: 760px;
  color: var(--ink-soft);
  line-height: 1.65;
}

.fraction-rule-form {
  display: grid;
  gap: 1rem;
  max-width: 760px;
  margin-top: 1.5rem;
}

.rule-blank {
  display: grid;
  gap: 0.5rem;
}

.rule-blank label {
  font-weight: 800;
}

.rule-blank select {
  width: 100%;
  min-height: 48px;
  padding: 0.65rem 0.8rem;
  border: 1px solid var(--line);
  background: var(--white);
  color: var(--ink);
}

.fraction-skill-results {
  display: grid;
  gap: 0.65rem;
  margin: 1rem 0 0;
  padding: 0;
  list-style: none;
}

.fraction-skill-results li {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 0.75rem;
  padding-bottom: 0.65rem;
  border-bottom: 1px solid var(--paper-deep);
}

.fraction-skill-results strong {
  color: var(--coral-dark);
}

.fraction-record-card {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  align-items: center;
  margin-block: 1.5rem;
  padding: 1.25rem;
  border: 2px solid var(--ink);
  background: var(--paper);
}

.fraction-record-card span {
  font-family: ui-monospace, "SFMono-Regular", monospace;
  font-size: clamp(1.5rem, 5vw, 2.5rem);
  font-weight: 800;
}

.fraction-set-model {
  display: grid;
  grid-template-columns: repeat(4, minmax(3rem, 1fr));
  gap: 0.75rem;
  max-width: 34rem;
  margin-block: 1.5rem;
}

.fraction-set-item {
  display: grid;
  width: 3.4rem;
  min-height: 3.4rem;
  place-items: center;
  justify-self: center;
  border: 2px solid var(--ink);
  border-radius: 999px;
  background: var(--paper);
  font-weight: 800;
}

.fraction-set-item:nth-child(3n + 1) {
  width: 3.2rem;
  min-height: 3.2rem;
}

.fraction-set-item:nth-child(4n) {
  width: 3.55rem;
  min-height: 3.55rem;
}

.fraction-set-item--selected {
  background: repeating-linear-gradient(
    135deg,
    #c7e0ef 0 6px,
    #9fc9df 6px 12px
  );
  box-shadow: inset 0 -0.3rem 0 #477f9d;
}

.video-cue {
  border-inline-start: 0.3rem solid var(--sage);
  padding-inline-start: 1rem;
}

#fraction-practice-form .secondary-button:disabled {
  cursor: not-allowed;
  opacity: 0.6;
}

#fraction-practice-form .secondary-button:disabled:hover {
  color: var(--ink);
  background: transparent;
}

@media (max-width: 760px) {
  .experiment-paths,
  .partition-compare,
  .fraction-option-diagrams {
    grid-template-columns: 1fr;
  }

  .fraction-strip {
    overflow-x: auto;
  }
}

@media (max-width: 420px) {
  .fraction-set-model {
    grid-template-columns: repeat(4, minmax(2.5rem, 1fr));
    gap: 0.45rem;
  }
}

@media (prefers-reduced-motion: reduce) {
  .fraction-part {
    transition: none;
  }
}

/* Measurement history and knowledge-relation node */
.history-scene {
  display: grid;
  gap: 12px;
  margin: 24px 0;
  padding: 20px;
  border: 1px solid var(--line);
  background: rgb(255 253 248 / 72%);
}

.history-scene p {
  margin: 0;
  line-height: 1.65;
}

.cubit-rod {
  width: min(100%, 525px);
  min-height: 76px;
  border: 2px solid var(--ink);
  background:
    repeating-linear-gradient(90deg, transparent 0 calc(100% / 7 - 2px), var(--ink) calc(100% / 7 - 2px) calc(100% / 7)),
    linear-gradient(var(--paper), var(--paper-deep));
  box-shadow: inset 0 -12px 0 rgb(215 163 58 / 26%);
}

.history-person {
  margin: 24px 0;
  padding: 16px 18px;
  border-left: 4px solid var(--mustard);
  background: var(--sage-pale);
}

.history-person strong {
  color: var(--ink);
}

.history-person p {
  margin: 8px 0 0;
  color: var(--ink);
  line-height: 1.65;
}

.history-more {
  margin: 24px 0;
  border-block: 1px solid var(--line);
}

.history-more summary {
  display: flex;
  align-items: center;
  min-height: 44px;
  cursor: pointer;
  font-weight: 750;
}

.history-more summary:focus-visible {
  outline: 3px solid var(--coral-dark);
  outline-offset: 3px;
}

.history-more p {
  margin: 0 0 8px;
  color: var(--ink-soft);
  line-height: 1.65;
}

.history-more a {
  display: inline-flex;
  align-items: center;
  min-height: 44px;
  color: var(--coral-dark);
  font-weight: 750;
}

.concept-path {
  margin: 24px 0;
  padding: 18px;
  border: 1px solid var(--line);
  border-left: 4px solid var(--coral);
  background: var(--white);
}

.concept-path h3 {
  margin-top: 0;
}

.concept-path p {
  margin-bottom: 0;
  line-height: 1.75;
}

.concept-transfer-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin-top: 16px;
}

.concept-transfer-grid span {
  padding: 14px;
  border: 1px solid var(--line);
  background: var(--paper);
  line-height: 1.55;
}

@media (max-width: 760px) {
  .concept-transfer-grid {
    grid-template-columns: 1fr;
  }
}

/* Generic Grade 2–3 concept lesson */
.generic-lesson {
  min-height: 620px;
  padding: clamp(28px, 5vw, 62px);
  border: 1px solid var(--line);
  background:
    linear-gradient(90deg, rgb(83 104 82 / 4%) 1px, transparent 1px) 0 0 / 32px 32px,
    linear-gradient(rgb(83 104 82 / 4%) 1px, transparent 1px) 0 0 / 32px 32px,
    var(--white);
  box-shadow: var(--shadow);
}

.generic-stage-header h2,
.generic-lesson > h2,
.experiment-heading h2 {
  max-width: 780px;
  margin: 0;
  font-family: "STKaiti", "KaiTi", serif;
  font-size: clamp(32px, 4.5vw, 54px);
  line-height: 1.18;
}

.stage-intro {
  max-width: 780px;
  margin-block: 28px;
}

.origin-type {
  display: inline-block;
  padding: 7px 11px;
  border-left: 3px solid var(--sage);
  background: var(--sage-pale);
  font-size: 13px;
  font-weight: 800;
}

.lead-question,
.core-explanation,
.experiment-prompt {
  max-width: 760px;
  margin: 24px 0;
  font-size: clamp(18px, 2.2vw, 24px);
  line-height: 1.75;
}

.choice-button {
  display: flex;
  justify-content: space-between;
  gap: 18px;
  align-items: center;
}

.choice-button i {
  color: var(--coral-dark);
  font-style: normal;
  font-size: 22px;
}

.quiet-note {
  max-width: 720px;
  margin-top: 25px;
  color: var(--ink-soft);
  line-height: 1.7;
}

.reveal-card,
.rule-card,
.video-pending,
.delayed-task,
.child-words {
  max-width: 800px;
  margin: 24px 0 34px;
  padding: 22px 24px;
  border-left: 5px solid var(--mustard);
  background: #fbf6e8;
  line-height: 1.7;
}

.reveal-card p:not(.eyebrow) {
  color: var(--ink-soft);
}

.reveal-card strong,
.rule-card {
  font-size: clamp(18px, 2vw, 23px);
}

.rule-card span {
  display: block;
  margin-bottom: 8px;
  color: var(--coral-dark);
  font-size: 12px;
  font-weight: 800;
  letter-spacing: 0.08em;
}

.representation-row {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: center;
  margin: 28px 0;
}

.representation-row span {
  padding: 14px 18px;
  border: 1px solid var(--line);
  background: var(--paper);
  font-weight: 800;
}

.representation-row i {
  color: var(--coral-dark);
  font-style: normal;
}

.experiment-card {
  max-width: 850px;
  margin-bottom: 30px;
  padding: clamp(22px, 4vw, 38px);
  border: 2px solid var(--ink);
  background: var(--paper);
  box-shadow: 8px 8px 0 var(--sage);
}

.experiment-heading {
  display: flex;
  gap: 16px;
  align-items: flex-start;
}

.experiment-heading > span {
  color: var(--coral-dark);
  font-size: 30px;
}

.experiment-heading h2 {
  font-size: clamp(27px, 4vw, 42px);
}

.experiment-options,
.tally-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.experiment-options button,
.experiment-action,
.tally-grid button,
.experiment-steps button {
  min-height: 52px;
  padding: 13px 16px;
  border: 1px solid var(--ink);
  background: var(--white);
  cursor: pointer;
  font-weight: 750;
}

.experiment-options button[aria-pressed="true"],
.experiment-options button:hover,
.experiment-action:hover,
.tally-grid button:hover,
.experiment-steps button:hover {
  background: var(--sage-pale);
}

.experiment-success {
  margin: 22px 0 0;
  padding: 15px 18px;
  border-left: 4px solid var(--sage);
  background: #edf5eb;
  line-height: 1.65;
}

.experiment-steps {
  display: grid;
  gap: 10px;
  padding: 0;
  list-style: none;
}

.experiment-steps li {
  display: grid;
  grid-template-columns: 34px minmax(0, 1fr);
  gap: 12px;
  align-items: center;
}

.experiment-steps li > span {
  display: grid;
  width: 32px;
  height: 32px;
  place-items: center;
  border: 1px solid var(--ink);
  border-radius: 50%;
}

.experiment-steps p {
  margin: 0;
  padding: 13px 16px;
  color: var(--ink-soft);
}

.experiment-steps .is-done p,
.experiment-steps .is-done span {
  color: var(--ink);
  background: var(--sage-pale);
}

.place-value-tray,
.unit-repeat-model {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-bottom: 18px;
}

.place-value-tray > div {
  display: grid;
  min-width: 96px;
  min-height: 96px;
  place-items: center;
  align-content: center;
  border: 2px solid var(--ink);
  background: var(--white);
}

.place-value-tray strong {
  font-size: 32px;
}

.unit-repeat-model span {
  display: grid;
  min-width: 58px;
  min-height: 58px;
  place-items: center;
  border: 2px dashed var(--line);
  color: var(--ink-soft);
  background: var(--white);
  font-size: 12px;
}

.unit-repeat-model .is-filled {
  border-style: solid;
  border-color: var(--coral-dark);
  background: #fff0e8;
}

.toggle-grid {
  display: grid;
  grid-template-columns: repeat(var(--grid-columns), minmax(44px, 70px));
  gap: 6px;
  margin-bottom: 12px;
}

.toggle-grid button {
  aspect-ratio: 1;
  min-width: 44px;
  border: 1px solid var(--ink);
  background: var(--white);
  cursor: pointer;
}

.toggle-grid button[aria-pressed="true"] {
  background: repeating-linear-gradient(135deg, var(--sage-pale) 0 7px, var(--sage) 7px 14px);
}

.tally-grid button {
  display: flex;
  justify-content: space-between;
  gap: 16px;
}

.tally-grid strong {
  color: var(--coral-dark);
  font-size: 22px;
}

.lesson-video {
  display: block;
  width: min(100%, 760px);
  max-height: 520px;
  margin: 28px 0;
  background: #17201c;
  box-shadow: 8px 8px 0 var(--sage);
}

.video-pending strong {
  display: block;
  margin-bottom: 9px;
}

.video-source {
  color: var(--ink-soft);
  line-height: 1.6;
}

.inline-action {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  color: inherit;
  text-decoration: none;
}

.relation-summary-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
  max-width: 820px;
}

.relation-summary-grid section,
.connection-list {
  padding: 20px;
  border: 1px solid var(--line);
  background: var(--paper);
}

.relation-summary-grid h3,
.connection-list h3 {
  margin-top: 0;
}

.relation-summary-grid ul,
.connection-list ul {
  padding-left: 20px;
  line-height: 1.7;
}

.connection-list {
  max-width: 820px;
  margin-top: 14px;
}

.connection-list li span {
  display: block;
  color: var(--coral-dark);
  font-size: 12px;
  font-weight: 800;
}

.connection-list li p {
  margin-top: 4px;
  color: var(--ink-soft);
}

.practice-heading {
  display: flex;
  justify-content: space-between;
  gap: 20px;
  align-items: end;
}

.practice-heading > span {
  padding: 8px 12px;
  border: 1px solid var(--line);
  font-weight: 800;
}

#generic-practice-form {
  max-width: 840px;
  margin-top: 28px;
}

.practice-fieldset {
  margin: 0;
  padding: 0;
  border: 0;
}

.practice-fieldset[aria-invalid="true"] .practice-options {
  padding-left: 12px;
  border-left: 4px solid var(--coral-dark);
}

.practice-fieldset legend {
  margin-bottom: 22px;
  font-size: clamp(19px, 2.3vw, 25px);
  font-weight: 750;
  line-height: 1.6;
}

.practice-option--selected {
  border-color: var(--coral-dark);
  background: #fff0e8;
}

.practice-hints {
  max-width: 720px;
  padding: 0;
  list-style: none;
}

.practice-hints li,
.practice-feedback,
.lesson-message {
  margin-top: 13px;
  padding: 14px 17px;
  border-left: 4px solid var(--mustard);
  background: #fff8e9;
  line-height: 1.65;
}

.practice-hints strong {
  display: block;
  color: var(--coral-dark);
}

.practice-feedback--correct {
  border-color: var(--sage);
  background: #edf5eb;
}

.practice-feedback--wrong,
.lesson-message {
  border-color: var(--coral-dark);
  background: #fff0eb;
}

.explanation-field {
  display: grid;
  gap: 9px;
  max-width: 760px;
  margin: 24px 0;
  font-weight: 800;
}

.explanation-field textarea {
  width: 100%;
  padding: 16px;
  border: 2px solid var(--ink);
  border-radius: 0;
  color: var(--ink);
  background: var(--paper);
  line-height: 1.7;
  resize: vertical;
}

.completion-mark {
  display: grid;
  width: 64px;
  height: 64px;
  margin-bottom: 22px;
  place-items: center;
  border-radius: 50%;
  color: var(--white);
  background: var(--ink);
  font-size: 32px;
}

.child-words blockquote {
  margin: 0;
  font-family: "STKaiti", "KaiTi", serif;
  font-size: clamp(20px, 2.7vw, 30px);
}

.delayed-task {
  border-color: var(--sage);
  background: var(--sage-pale);
}

.delayed-task h3 {
  margin-top: 0;
}

.text-button {
  min-height: 44px;
  padding: 10px 4px;
  border: 0;
  color: var(--coral-dark);
  background: transparent;
  cursor: pointer;
  font-weight: 800;
  text-decoration: underline;
  text-underline-offset: 4px;
}

.missing-lesson p {
  max-width: 660px;
  line-height: 1.75;
}

@media (max-width: 760px) {
  .generic-lesson {
    min-height: 0;
    padding: 30px 22px 38px;
  }

  .experiment-options,
  .tally-grid,
  .relation-summary-grid {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 520px) {
  .generic-lesson .button-row {
    align-items: stretch;
    flex-direction: column;
  }

  .generic-lesson .button-row > * {
    width: 100%;
  }

  .representation-row i {
    transform: rotate(90deg);
  }
}

@media (prefers-reduced-motion: reduce) {
  .progress-track span,
  .choice-button,
  .experiment-options button,
  .experiment-action {
    transition: none;
  }
}

/* Grade 2–3 course home */
.course-page {
  background:
    radial-gradient(circle at 85% 6%, rgb(215 163 58 / 16%), transparent 25rem),
    var(--paper);
}

.course-topbar {
  position: sticky;
  top: 0;
  z-index: 5;
  display: grid;
  grid-template-columns: 260px minmax(340px, 1fr) auto;
  min-height: 76px;
  align-items: center;
  border-bottom: 1px solid var(--line);
  background: rgb(255 253 248 / 90%);
  backdrop-filter: blur(16px);
}

.course-topbar .brand {
  min-height: 76px;
}

.course-primary-nav {
  display: flex;
  gap: 8px;
  align-items: center;
  padding-inline: 24px;
}

.course-primary-nav a,
.course-primary-nav button {
  min-height: 44px;
  padding: 11px 15px;
  border: 0;
  color: var(--ink);
  background: transparent;
  cursor: pointer;
  font-weight: 800;
  text-decoration: none;
}

.course-primary-nav a[aria-current="page"] {
  border-bottom: 3px solid var(--coral-dark);
}

.course-primary-nav button:hover,
.course-primary-nav a:hover {
  background: var(--paper-deep);
}

.course-term {
  margin: 0;
  padding-right: 28px;
  color: var(--ink-soft);
  font-size: 13px;
  font-weight: 700;
}

.course-main {
  width: min(1240px, calc(100% - 48px));
  margin: 0 auto;
  padding: clamp(42px, 7vw, 88px) 0 80px;
}

.course-summary {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(250px, 330px);
  gap: clamp(32px, 7vw, 90px);
  align-items: end;
  margin-bottom: 54px;
}

.course-summary h1 {
  margin: 0;
  font-family: "STKaiti", "KaiTi", serif;
  font-size: clamp(44px, 7vw, 82px);
  line-height: 1.08;
}

.course-summary > div > p:not(.eyebrow) {
  max-width: 700px;
  color: var(--ink-soft);
  font-size: clamp(16px, 1.8vw, 20px);
  line-height: 1.8;
}

.course-progress-card {
  padding: 25px;
  border: 1px solid var(--ink);
  background: var(--white);
  box-shadow: 7px 7px 0 var(--sage);
}

.course-progress-card strong {
  font-family: ui-monospace, "SFMono-Regular", monospace;
  font-size: 42px;
}

.course-progress-card strong span {
  color: var(--ink-soft);
  font-size: 20px;
}

.course-progress-card p {
  margin: 6px 0 18px;
  color: var(--ink-soft);
  font-size: 13px;
}

.course-modules {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 24px;
}

.course-module {
  overflow: hidden;
  border: 1px solid var(--line);
  background: var(--white);
  box-shadow: 0 14px 36px rgb(48 53 44 / 7%);
}

.course-module-heading {
  display: grid;
  grid-template-columns: 75px 1fr;
  gap: 18px;
  align-items: center;
  min-height: 105px;
  padding: 20px 24px;
  border-bottom: 1px solid var(--line);
  background: var(--paper-deep);
}

.course-module-heading > span {
  color: var(--coral-dark);
  font-family: ui-monospace, "SFMono-Regular", monospace;
  font-size: 12px;
  font-weight: 800;
}

.course-module-heading h2,
.course-module-heading p {
  margin: 0;
}

.course-module-heading h2 {
  font-family: "STKaiti", "KaiTi", serif;
  font-size: clamp(23px, 2.5vw, 31px);
}

.course-module-heading p {
  margin-top: 4px;
  color: var(--ink-soft);
  font-size: 12px;
}

.course-concept-list {
  margin: 0;
  padding: 0;
  list-style: none;
}

.course-concept + .course-concept {
  border-top: 1px solid var(--paper-deep);
}

.course-concept a {
  display: grid;
  grid-template-columns: 42px minmax(0, 1fr) auto;
  gap: 14px;
  align-items: center;
  min-height: 84px;
  padding: 14px 20px;
  color: var(--ink);
  text-decoration: none;
  transition: background 180ms ease, box-shadow 180ms ease;
}

.course-concept a:hover {
  background: #fff8ef;
  box-shadow: inset 5px 0 0 var(--coral);
}

.course-index {
  color: var(--ink-soft);
  font-family: ui-monospace, "SFMono-Regular", monospace;
  font-size: 13px;
}

.course-concept-copy {
  min-width: 0;
}

.course-concept-copy strong,
.course-concept-copy small {
  display: block;
}

.course-concept-copy strong {
  line-height: 1.45;
}

.course-concept-copy small {
  margin-top: 5px;
  color: var(--ink-soft);
  font-size: 11px;
}

.course-state {
  padding: 6px 8px;
  border: 1px solid var(--line);
  color: var(--ink-soft);
  font-size: 11px;
  font-weight: 800;
  white-space: nowrap;
}

.course-concept--recommended a {
  background: #fff4df;
  box-shadow: inset 5px 0 0 var(--mustard);
}

.course-concept--recommended .course-state {
  border-color: var(--coral-dark);
  color: var(--white);
  background: var(--coral-dark);
}

.course-concept--complete .course-index::after {
  content: " ✓";
  color: var(--sage);
  font-weight: 900;
}

.course-concept--complete .course-state {
  border-color: var(--sage);
  color: var(--ink);
  background: var(--sage-pale);
}

.course-concept--supported .course-state {
  border-color: var(--mustard);
  background: #fff8e9;
}

.map-entry-card {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: 30px;
  align-items: center;
  margin-top: 40px;
  padding: clamp(25px, 4vw, 42px);
  border: 2px solid var(--ink);
  background: var(--sage-pale);
}

.map-entry-card h2 {
  margin: 0;
  font-family: "STKaiti", "KaiTi", serif;
  font-size: clamp(28px, 4vw, 42px);
}

.map-entry-card p:not(.eyebrow) {
  max-width: 750px;
  margin-bottom: 0;
  line-height: 1.7;
}

.detail-content-status {
  margin: -8px 0 20px;
  color: var(--ink-soft);
  font-size: 12px;
  font-weight: 750;
}

@media (max-width: 920px) {
  .course-topbar {
    grid-template-columns: 220px 1fr;
  }

  .course-term {
    display: none;
  }

  .course-summary {
    grid-template-columns: 1fr;
  }

  .course-progress-card {
    max-width: 420px;
  }
}

@media (max-width: 760px) {
  .course-topbar {
    position: static;
    grid-template-columns: 1fr;
  }

  .course-topbar .brand {
    min-height: 66px;
    border-right: 0;
    border-bottom: 1px solid var(--line);
  }

  .course-primary-nav {
    overflow-x: auto;
    padding: 8px 16px;
  }

  .course-main {
    width: min(100% - 28px, 620px);
    padding-top: 40px;
  }

  .course-modules,
  .map-entry-card {
    grid-template-columns: 1fr;
  }
}

@media (max-width: 460px) {
  .course-module-heading {
    grid-template-columns: 1fr;
    gap: 7px;
  }

  .course-concept a {
    grid-template-columns: 34px minmax(0, 1fr);
  }

  .course-state {
    grid-column: 2;
    justify-self: start;
  }
}

@media (prefers-reduced-motion: reduce) {
  .course-concept a,
  .course-primary-nav a,
  .course-primary-nav button {
    transition: none;
  }
}