:root {
  color-scheme: light;
  --bg: #f5f6f8;
  --surface: #ffffff;
  --surface-soft: #eef4f6;
  --ink: #0f172a;
  --muted: #475569;
  --brand: #0e7490;
  --brand-strong: #0b5c73;
  --brand-soft: #e0f2f6;
  --accent: #6d28d9;
  --accent-soft: #f1ebfe;
  --line: #e2e8f0;
  --danger: #b42318;
  --danger-soft: #fdeceb;
  --ok: #047857;
  --ok-soft: #e6f5ec;
  --focus: #0e7490;
  --radius: 16px;
  --radius-lg: 20px;
  --shadow: 0 18px 40px rgba(15, 23, 42, 0.08);
  --font: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: var(--font);
  font-size: 1rem;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

img,
svg {
  max-width: 100%;
  height: auto;
}

a {
  color: var(--brand-strong);
  text-underline-offset: 0.18em;
}

a:hover {
  color: var(--brand);
}

:focus-visible {
  outline: 3px solid var(--focus);
  outline-offset: 3px;
}

.skip-link {
  position: absolute;
  left: -999px;
  top: 0;
  z-index: 100;
  background: var(--ink);
  color: #fff;
  padding: 0.75rem 1rem;
  border-radius: 0 0 var(--radius) 0;
}

.skip-link:focus {
  left: 0;
}

.wrap {
  width: min(1080px, 100% - 2.5rem);
  margin-inline: auto;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  background: rgba(251, 250, 247, 0.94);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--line);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  min-height: 4.25rem;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.6rem;
  color: var(--ink);
  font-weight: 750;
  font-size: 1.1rem;
  text-decoration: none;
  letter-spacing: -0.01em;
}

.brand img {
  width: 36px;
  height: 36px;
}

.site-nav {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.site-nav a {
  color: var(--muted);
  text-decoration: none;
  padding: 0.45rem 0.7rem;
  border-radius: 999px;
  font-weight: 600;
  font-size: 0.94rem;
}

.site-nav a:hover,
.site-nav a:focus-visible {
  background: var(--surface-soft);
  color: var(--brand-strong);
}

main {
  padding-block: 2rem 3.5rem;
}

h1,
h2,
h3,
h4 {
  line-height: 1.2;
  letter-spacing: -0.02em;
  margin: 0 0 0.6rem;
}

h1 {
  font-size: clamp(2rem, 4.5vw, 3rem);
}

h2 {
  font-size: clamp(1.5rem, 3vw, 2rem);
  margin-top: 2.4rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--line);
}

h3 {
  font-size: 1.2rem;
  margin-top: 1.6rem;
}

p {
  margin: 0 0 1rem;
}

ul,
ol {
  padding-left: 1.35rem;
}

li {
  margin-bottom: 0.35rem;
}

.hero {
  display: grid;
  gap: 1.5rem;
  padding: clamp(1.5rem, 4vw, 3rem);
  border-radius: calc(var(--radius) + 8px);
  background:
    radial-gradient(circle at 100% 0%, rgba(232, 163, 61, 0.22), transparent 45%),
    linear-gradient(135deg, var(--brand-soft), #f8fbf9 70%);
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}

.hero h1 {
  max-width: 18ch;
}

.hero p {
  max-width: 62ch;
  color: var(--muted);
  font-size: 1.08rem;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.7rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  background: var(--brand);
  color: #fff;
  border: 2px solid var(--brand);
  border-radius: 999px;
  padding: 0.6rem 1.1rem;
  font: inherit;
  font-weight: 700;
  text-decoration: none;
  cursor: pointer;
}

.btn:hover {
  background: var(--brand-strong);
  border-color: var(--brand-strong);
  color: #fff;
}

.btn--ghost {
  background: transparent;
  color: var(--brand-strong);
  border-color: var(--brand);
}

.btn--ghost:hover {
  background: var(--brand-soft);
  color: var(--brand-strong);
}

.badge {
  display: inline-flex;
  align-items: center;
  gap: 0.25rem;
  background: var(--surface-soft);
  color: var(--brand-strong);
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 0.18rem 0.6rem;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.01em;
}

.badge--accent {
  background: var(--accent-soft);
  border-color: #f2d3a2;
  color: #7a4c0b;
}

.badge--muted {
  background: #f5f5f3;
  color: var(--muted);
}

.filters {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(170px, 1fr));
  gap: 0.9rem;
  padding: 1rem;
  margin: 1rem 0 1.2rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
}

.filters label {
  display: grid;
  gap: 0.3rem;
  font-size: 0.82rem;
  font-weight: 700;
  color: var(--muted);
}

.filters select,
.filters input {
  width: 100%;
  padding: 0.55rem 0.65rem;
  border: 1px solid var(--line);
  border-radius: 9px;
  background: var(--bg);
  color: var(--ink);
  font: inherit;
}

.catalog-count {
  color: var(--muted);
  font-size: 0.92rem;
}

.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(270px, 1fr));
  gap: 1rem;
  margin-top: 1rem;
}

.topic-card {
  display: flex;
  flex-direction: column;
  gap: 0.7rem;
  padding: 1.15rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  box-shadow: 0 4px 14px rgba(20, 40, 34, 0.04);
  transition: transform 160ms ease, box-shadow 160ms ease, border-color 160ms ease;
}

.topic-card:hover {
  transform: translateY(-2px);
  border-color: #b9d6cc;
  box-shadow: var(--shadow);
}

.topic-card h3 {
  margin: 0;
  font-size: 1.18rem;
}

.topic-card h3 a {
  color: var(--ink);
  text-decoration: none;
}

.topic-card h3 a:hover {
  color: var(--brand-strong);
  text-decoration: underline;
}

.topic-card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
}

.topic-card .card-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
}

.topic-card .card-link {
  margin-top: auto;
  font-weight: 700;
  text-decoration: none;
}

.empty-state {
  margin-top: 1rem;
  padding: 1rem;
  border: 1px dashed var(--line);
  border-radius: var(--radius);
  color: var(--muted);
  background: var(--surface);
}

.breadcrumbs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  align-items: center;
  margin-bottom: 1rem;
  color: var(--muted);
  font-size: 0.9rem;
}

.breadcrumbs a {
  color: var(--muted);
}

.breadcrumbs span[aria-current="page"] {
  color: var(--ink);
  font-weight: 650;
}

.topic-header {
  padding: clamp(1.3rem, 3vw, 2.2rem);
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: calc(var(--radius) + 4px);
  box-shadow: var(--shadow);
}

.topic-header h1 {
  max-width: 22ch;
}

.topic-subtitle {
  font-size: 1.15rem;
  color: var(--muted);
  max-width: 60ch;
}

.topic-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin: 1rem 0;
}

.topic-summary {
  max-width: 68ch;
  font-size: 1.05rem;
}

.objectives {
  margin-top: 1.2rem;
  padding: 1rem 1.1rem;
  background: var(--surface-soft);
  border-radius: var(--radius);
}

.objectives h2,
.key-concepts h2 {
  margin: 0 0 0.5rem;
  padding: 0;
  border: 0;
  font-size: 1.05rem;
}

.key-concepts {
  margin-top: 1rem;
  padding: 1rem 1.1rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
}

.key-concepts dl {
  margin: 0;
}

.key-concepts dt {
  font-weight: 750;
  margin-top: 0.55rem;
}

.key-concepts dd {
  margin: 0.1rem 0 0;
  color: var(--muted);
}

.toc {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin: 1.2rem 0 1.6rem;
  padding: 0.9rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
}

.toc a {
  padding: 0.35rem 0.65rem;
  border-radius: 999px;
  background: var(--surface-soft);
  color: var(--brand-strong);
  text-decoration: none;
  font-size: 0.88rem;
  font-weight: 650;
}

.toc a:hover {
  background: var(--brand-soft);
}

.topic-sections > section {
  scroll-margin-top: 5.5rem;
}

.section-intro {
  max-width: 70ch;
  color: var(--muted);
}

.callout {
  margin: 1rem 0;
  padding: 0.9rem 1rem;
  border-left: 5px solid var(--brand);
  background: var(--surface-soft);
  border-radius: 0 var(--radius) var(--radius) 0;
}

.callout strong {
  display: block;
  margin-bottom: 0.2rem;
}

.callout--warning {
  border-left-color: var(--accent);
  background: var(--accent-soft);
}

.callout--tip {
  border-left-color: var(--brand);
  background: var(--brand-soft);
}

.steps {
  counter-reset: step;
  list-style: none;
  padding: 0;
}

.steps li {
  position: relative;
  padding-left: 2.2rem;
  margin-bottom: 0.7rem;
}

.steps li::before {
  counter-increment: step;
  content: counter(step);
  position: absolute;
  left: 0;
  top: 0.05rem;
  width: 1.6rem;
  height: 1.6rem;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--brand);
  color: #fff;
  font-size: 0.82rem;
  font-weight: 800;
}

.example {
  margin: 1.2rem 0;
  padding: 1rem 1.1rem;
  background: #f7faf8;
  border: 1px solid var(--line);
  border-radius: var(--radius);
}

.example h3 {
  margin-top: 0;
}

.example-lines {
  list-style: none;
  padding: 0;
  margin: 0;
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  font-size: 0.98rem;
}

.example-lines li {
  padding: 0.25rem 0;
  border-bottom: 1px dashed var(--line);
}

.example-lines li:last-child {
  border-bottom: 0;
}

.table-wrap {
  overflow-x: auto;
  margin: 1rem 0;
}

.data-table {
  width: 100%;
  border-collapse: collapse;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  overflow: hidden;
  font-size: 0.95rem;
}

.data-table caption {
  caption-side: top;
  text-align: left;
  font-weight: 750;
  padding: 0 0 0.5rem;
}

.data-table th,
.data-table td {
  padding: 0.6rem 0.7rem;
  border-bottom: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

.data-table th {
  background: var(--surface-soft);
  font-size: 0.82rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--muted);
}

.data-table tr:last-child td {
  border-bottom: 0;
}

.common-errors {
  margin-top: 1.2rem;
  padding: 1rem;
  background: var(--danger-soft);
  border: 1px solid #f3c9c6;
  border-radius: var(--radius);
}

.common-errors h3 {
  margin-top: 0;
  color: var(--danger);
}

.common-errors dl {
  margin: 0;
}

.common-errors dt {
  font-weight: 750;
  margin-top: 0.6rem;
}

.common-errors dd {
  margin: 0.1rem 0 0;
}

.exercise {
  margin: 1rem 0;
  padding: 1rem 1.1rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
}

.exercise h3 {
  margin-top: 0;
  font-size: 1.05rem;
}

.options {
  display: grid;
  gap: 0.45rem;
  margin: 0.8rem 0;
}

.option {
  text-align: left;
  padding: 0.55rem 0.75rem;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--bg);
  color: var(--ink);
  font: inherit;
  cursor: pointer;
}

.option:hover {
  border-color: var(--brand);
  background: var(--surface-soft);
}

.option.is-correct {
  border-color: var(--ok);
  background: var(--ok-soft);
  font-weight: 700;
}

.option.is-incorrect {
  border-color: var(--danger);
  background: var(--danger-soft);
}

.fill-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  align-items: center;
  margin: 0.7rem 0;
}

.fill-input {
  flex: 1 1 220px;
  padding: 0.55rem 0.65rem;
  border: 1px solid var(--line);
  border-radius: 9px;
  background: var(--bg);
  color: var(--ink);
  font: inherit;
}

.fill-input.is-correct {
  border-color: var(--ok);
  background: var(--ok-soft);
}

.fill-input.is-incorrect {
  border-color: var(--danger);
  background: var(--danger-soft);
}

.feedback {
  min-height: 1.5rem;
  margin: 0.5rem 0 0;
  font-weight: 700;
}

.feedback.is-correct {
  color: var(--ok);
}

.feedback.is-incorrect {
  color: var(--danger);
}

.explanation {
  margin-top: 0.6rem;
  padding: 0.7rem 0.8rem;
  background: var(--surface-soft);
  border-radius: 10px;
  color: var(--muted);
  font-size: 0.93rem;
}

.order-list {
  list-style: none;
  padding: 0;
  margin: 0.8rem 0;
  display: grid;
  gap: 0.45rem;
}

.order-list li {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.45rem 0.6rem;
  background: var(--bg);
  border: 1px solid var(--line);
  border-radius: 10px;
}

.order-list .handle {
  flex: 1;
}

.order-list button {
  width: 2rem;
  height: 2rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--ink);
  font: inherit;
  cursor: pointer;
}

.order-list button:hover {
  background: var(--surface-soft);
}

.solution {
  margin-top: 0.7rem;
  padding: 0.65rem 0.8rem;
  border: 1px dashed var(--line);
  border-radius: 10px;
  background: var(--bg);
}

.solution summary {
  cursor: pointer;
  font-weight: 700;
  color: var(--brand-strong);
}

.quiz {
  display: grid;
  gap: 1rem;
}

.quiz fieldset {
  margin: 0;
  padding: 1rem 1.1rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
}

.quiz legend {
  font-weight: 750;
  padding: 0 0.35rem;
}

.quiz label {
  display: block;
  padding: 0.35rem 0;
  cursor: pointer;
}

.quiz input[type="text"] {
  width: 100%;
  max-width: 420px;
  padding: 0.55rem 0.65rem;
  border: 1px solid var(--line);
  border-radius: 9px;
  font: inherit;
}

.quiz-result {
  margin-top: 1rem;
  padding: 1rem 1.1rem;
  border-radius: var(--radius);
  background: var(--surface-soft);
  font-weight: 700;
}

.quiz-result.is-pass {
  background: var(--ok-soft);
  color: var(--ok);
}

.quiz-result.is-fail {
  background: var(--danger-soft);
  color: var(--danger);
}

.download-grid,
.multimedia-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1rem;
  margin-top: 1rem;
}

.download-card,
.multimedia-card {
  display: flex;
  flex-direction: column;
  gap: 0.5rem;
  padding: 1rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
}

.download-card h3,
.multimedia-card h3 {
  margin: 0;
  font-size: 1.05rem;
}

.download-card p,
.multimedia-card p {
  margin: 0;
  color: var(--muted);
  font-size: 0.93rem;
}

.download-card .btn {
  align-self: flex-start;
  margin-top: 0.3rem;
}

.multimedia-card img {
  width: 100%;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: #fff;
}

.reading-text {
  padding: 1.2rem 1.3rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
}

.reading-text h3 {
  margin-top: 0;
}

.reading-text p {
  font-size: 1.08rem;
}

.glossary {
  margin-top: 1rem;
  padding: 1rem 1.1rem;
  background: var(--surface-soft);
  border-radius: var(--radius);
}

.glossary dl {
  margin: 0;
}

.glossary dt {
  font-weight: 750;
}

.glossary dd {
  margin: 0 0 0.45rem;
  color: var(--muted);
}

.reading-questions {
  margin-top: 1rem;
}

.reading-questions ol {
  padding-left: 1.3rem;
}

.reading-questions li {
  margin-bottom: 0.7rem;
}

.reading-questions details {
  margin-top: 0.2rem;
}

.resources {
  margin-top: 2.5rem;
}

.resource-list {
  display: grid;
  gap: 0.55rem;
  padding: 0;
  list-style: none;
}

.resource-list li {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  align-items: baseline;
  padding: 0.65rem 0.8rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 10px;
}

.resource-list .resource-type {
  font-size: 0.75rem;
  font-weight: 800;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--brand-strong);
}

.resource-list .resource-desc {
  color: var(--muted);
  font-size: 0.9rem;
}

.prev-next {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 0.8rem;
  margin-top: 2.5rem;
  padding-top: 1.2rem;
  border-top: 1px solid var(--line);
}

.prev-next a {
  display: inline-flex;
  flex-direction: column;
  gap: 0.1rem;
  padding: 0.7rem 0.9rem;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--surface);
  text-decoration: none;
  color: var(--ink);
  max-width: 48%;
}

.prev-next .dir {
  font-size: 0.78rem;
  color: var(--muted);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
}

.prose {
  max-width: 72ch;
}

.prose h1 {
  margin-bottom: 1rem;
}

.prose h2 {
  margin-top: 2rem;
}

.page-head h1 {
  margin-bottom: 0.5rem;
}

.search-panel {
  margin-top: 1rem;
}

.search-form {
  display: grid;
  gap: 0.4rem;
  padding: 1rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
}

.search-form label {
  font-weight: 700;
  font-size: 0.88rem;
  color: var(--muted);
}

.search-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.search-row input {
  flex: 1 1 260px;
  padding: 0.6rem 0.7rem;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--bg);
  color: var(--ink);
  font: inherit;
}

.site-footer {
  border-top: 1px solid var(--line);
  background: var(--surface);
  color: var(--muted);
  font-size: 0.9rem;
}

.footer-inner {
  padding-block: 1.4rem;
}

.footer-inner p {
  margin: 0.25rem 0;
}

.site-footer a {
  color: var(--muted);
}

@media (max-width: 640px) {
  .header-inner {
    align-items: flex-start;
    flex-direction: column;
    padding-block: 0.7rem;
  }

  .site-nav {
    width: 100%;
  }

  .site-nav a {
    padding: 0.4rem 0.55rem;
  }

  .prev-next a {
    max-width: 100%;
  }

  .topic-header h1 {
    max-width: none;
  }
}

/* ---------- App shell (ChatGPT-style) ---------- */

.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;
}

.app-shell {
  display: flex;
  min-height: 100vh;
}

.sidebar {
  position: sticky;
  top: 0;
  flex: 0 0 248px;
  width: 248px;
  height: 100vh;
  display: flex;
  flex-direction: column;
  background: #fbfbfc;
  border-right: 1px solid var(--line);
  z-index: 40;
}

.sidebar__head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  padding: 0.7rem 0.65rem 0.45rem;
}

.sidebar .brand {
  padding: 0.15rem 0.3rem;
  border-radius: 8px;
}

.sidebar .brand img {
  width: 26px;
  height: 26px;
}

.sidebar .brand span {
  font-size: 0.92rem;
}

.icon-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2.15rem;
  height: 2.15rem;
  padding: 0;
  border: 1px solid transparent;
  border-radius: 10px;
  background: transparent;
  color: var(--muted);
  font-size: 1.05rem;
  line-height: 1;
  cursor: pointer;
}

.icon-btn:hover {
  background: #eef1f5;
  color: var(--ink);
}

.sidebar__close {
  display: none;
}

.sidebar__quick {
  display: grid;
  gap: 0.1rem;
  padding: 0 0.55rem 0.35rem;
}

.quick-link {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  padding: 0.42rem 0.55rem;
  border-radius: 8px;
  color: var(--ink);
  font-size: 0.84rem;
  font-weight: 600;
  text-decoration: none;
}

.quick-link:hover {
  background: #eef1f5;
  color: var(--ink);
}

.quick-link__icon {
  font-size: 0.8rem;
}

.sidebar__scroll {
  flex: 1;
  overflow-y: auto;
  padding: 0.1rem 0.55rem 0.75rem;
  scrollbar-width: thin;
  scrollbar-color: #cbd5e1 transparent;
  scrollbar-gutter: stable;
}

.nav-section,
.nav-section--lead {
  margin: 0.85rem 0 0.32rem;
  padding: 0 0.6rem;
  color: var(--muted);
  font-size: 0.66rem;
  font-weight: 700;
  letter-spacing: 0.09em;
  text-transform: uppercase;
}

.year-nav {
  display: grid;
  gap: 0.05rem;
}

.year__summary:focus-visible,
.subject-link:focus-visible,
.quick-link:focus-visible {
  outline: 2px solid var(--brand);
  outline-offset: 1px;
}

.year {
  border-radius: 8px;
}

.year__summary {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.4rem 0.5rem;
  border-radius: 8px;
  color: var(--ink);
  font-size: 0.84rem;
  font-weight: 650;
  list-style: none;
  cursor: pointer;
  user-select: none;
}

.year__summary::-webkit-details-marker {
  display: none;
}

.year__summary:hover {
  background: #eef1f5;
}

.year__label {
  flex: 1;
  min-width: 0;
}

.year__count {
  min-width: 1.2rem;
  padding: 0.02rem 0.34rem;
  border-radius: 999px;
  background: #eef1f5;
  color: var(--muted);
  font-size: 0.66rem;
  font-weight: 700;
  text-align: center;
}

.year__chevron {
  flex: 0 0 auto;
  color: var(--muted);
  transition: transform 160ms ease;
}

.year[open] > .year__summary .year__chevron {
  transform: rotate(180deg);
}

.subject-list {
  margin: 0.05rem 0 0.3rem 0.45rem;
  padding: 0 0 0 0.45rem;
  border-left: 1px solid var(--line);
  list-style: none;
  display: grid;
  gap: 0.02rem;
}

.subject-link {
  display: flex;
  align-items: center;
  gap: 0.4rem;
  min-height: 1.9rem;
  padding: 0.3rem 0.42rem;
  border-radius: 7px;
  color: var(--ink);
  font-size: 0.78rem;
  line-height: 1.25;
  text-decoration: none;
}

.subject-link:hover {
  background: #eef1f5;
  color: var(--ink);
}

.subject-link.is-active {
  background: var(--brand-soft);
  color: var(--brand-strong);
  font-weight: 700;
  box-shadow: inset 2px 0 0 var(--brand);
}

.subject-link__icon {
  flex: 0 0 auto;
  width: 1.05rem;
  text-align: center;
  font-size: 0.76rem;
}

.subject-link__name {
  flex: 1;
  min-width: 0;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.subject-link__count {
  flex: 0 0 auto;
  min-width: 1.05rem;
  padding: 0 0.3rem;
  border-radius: 999px;
  background: #e2e8f0;
  color: var(--muted);
  font-size: 0.62rem;
  font-weight: 700;
  text-align: center;
}

.subject-link.is-active .subject-link__count {
  background: rgba(14, 116, 144, 0.16);
  color: var(--brand-strong);
}

.subject-link__flag {
  flex: 0 0 auto;
  color: var(--muted);
  font-size: 0.55rem;
  font-weight: 700;
  letter-spacing: 0.03em;
  text-transform: uppercase;
}

.sidebar__foot {
  display: grid;
  gap: 0.15rem;
  padding: 0.65rem 0.85rem 0.85rem;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.7rem;
}

.sidebar__foot a {
  color: var(--muted);
}

.sidebar-backdrop {
  display: none;
}

.app-main {
  flex: 1;
  min-width: 0;
  display: flex;
  flex-direction: column;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 30;
  display: flex;
  align-items: center;
  gap: 0.6rem;
  min-height: 3.75rem;
  padding: 0 1.5rem;
  background: rgba(255, 255, 255, 0.86);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--line);
}

.topbar__brand {
  color: var(--ink);
  font-weight: 750;
  text-decoration: none;
}

.topbar__sep {
  color: var(--line);
}

.topbar__section {
  color: var(--muted);
  font-size: 0.9rem;
}

.menu-toggle {
  display: none;
}

.content {
  flex: 1;
  display: flex;
  flex-direction: column;
  min-height: calc(100vh - 3.75rem);
  padding-block: 0;
}

.content-inner {
  flex: 1;
  width: 100%;
  max-width: 1080px;
  margin-inline: auto;
  padding: clamp(1.5rem, 4vw, 3rem) clamp(1.1rem, 3vw, 2.25rem);
}

.content-inner > :first-child {
  margin-top: 0;
}

/* ---------- Home / hero ---------- */

.home-hero {
  padding: clamp(1.5rem, 4vw, 3rem) 0 clamp(1.75rem, 4vw, 3rem);
  text-align: center;
}

.eyebrow {
  margin: 0 0 0.6rem;
  color: var(--brand);
  font-size: 0.74rem;
  font-weight: 750;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.home-hero h1 {
  margin: 0 auto 0.85rem;
  max-width: 20ch;
  font-size: clamp(2rem, 5vw, 3.1rem);
  line-height: 1.1;
  letter-spacing: -0.035em;
}

.home-hero > p:not(.eyebrow) {
  max-width: 58ch;
  margin: 0 auto 1.6rem;
  color: var(--muted);
  font-size: 1.02rem;
}

.hero-search {
  display: flex;
  gap: 0.5rem;
  width: min(620px, 100%);
  margin: 0 auto 1.25rem;
  padding: 0.4rem;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 999px;
  box-shadow: 0 12px 30px rgba(15, 23, 42, 0.06);
}

.hero-search input {
  flex: 1;
  min-width: 0;
  padding: 0.65rem 1rem;
  border: 0;
  background: transparent;
  color: var(--ink);
  font: inherit;
}

.hero-search input:focus {
  outline: none;
}

.hero-search .btn {
  border-radius: 999px;
}

.home-hero__stats {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.5rem;
}

.pill {
  padding: 0.35rem 0.8rem;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--surface);
  color: var(--muted);
  font-size: 0.82rem;
}

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

.section-head {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  gap: 1rem;
  flex-wrap: wrap;
  margin-bottom: 1.1rem;
}

.section-head h2 {
  margin: 0;
  font-size: 1.35rem;
  letter-spacing: -0.02em;
}

.section-head p {
  margin: 0;
  color: var(--muted);
  font-size: 0.9rem;
}

/* ---------- Cards (flexialabs style) ---------- */

.topic-grid {
  grid-template-columns: repeat(auto-fill, minmax(235px, 1fr));
  gap: 0.85rem;
  margin-top: 0;
}

.topic-card {
  position: relative;
  overflow: hidden;
  gap: 0.5rem;
  padding: 1.2rem 1.1rem 1.05rem;
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  background: var(--surface);
  box-shadow: 0 4px 14px rgba(15, 23, 42, 0.04);
}

.topic-card::before {
  content: "";
  position: absolute;
  inset: -40% 30% auto -30%;
  height: 180px;
  background: radial-gradient(circle at 30% 30%, rgba(14, 116, 144, 0.12), transparent 65%);
  pointer-events: none;
}

.topic-card:hover {
  transform: translateY(-5px);
  border-color: rgba(14, 116, 144, 0.24);
  box-shadow: 0 22px 45px rgba(15, 23, 42, 0.1);
}

.topic-card__icon {
  position: relative;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2.15rem;
  height: 2.15rem;
  margin-bottom: 0.1rem;
  border-radius: 11px;
  background: linear-gradient(135deg, var(--brand-soft), #f1ebfe);
  font-size: 1rem;
  line-height: 1;
}

.topic-card .card-meta {
  gap: 0.35rem;
}

.topic-card h3 {
  position: relative;
  font-size: 1.02rem;
  line-height: 1.3;
  letter-spacing: -0.015em;
}

.topic-card p {
  position: relative;
  font-size: 0.86rem;
  line-height: 1.5;
}

.topic-card__foot {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.6rem;
  margin-top: auto;
  padding-top: 0.35rem;
}

.topic-card__time {
  color: var(--muted);
  font-size: 0.72rem;
  font-weight: 600;
}

.topic-card .card-link {
  color: var(--brand-strong);
  font-size: 0.8rem;
  font-weight: 750;
}

.topic-card .card-link:hover {
  color: var(--brand);
}

/* ---------- Activity cards (0-3 years) ---------- */

.activity-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 0.95rem;
}

.activity-card {
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  background: var(--surface);
  padding: 1.15rem 1.15rem 1.05rem;
  box-shadow: 0 1px 2px rgba(15, 23, 42, 0.04);
}

.activity-card__head h3 {
  margin: 0;
  font-size: 1.02rem;
  letter-spacing: -0.01em;
}

.activity-card__meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.3rem 0.8rem;
  margin: 0.3rem 0 0;
  color: var(--muted);
  font-size: 0.76rem;
  font-weight: 600;
}

.activity-card__objective {
  margin: 0.55rem 0 0;
  color: var(--ink);
  font-size: 0.88rem;
  line-height: 1.55;
}

.activity-card__grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(210px, 1fr));
  gap: 0.7rem 1rem;
  margin-top: 0.8rem;
  padding-top: 0.8rem;
  border-top: 1px solid var(--line);
}

.activity-card__grid h4 {
  margin: 0 0 0.22rem;
  color: var(--brand-strong);
  font-size: 0.72rem;
  font-weight: 750;
  letter-spacing: 0.06em;
  text-transform: uppercase;
}

.activity-card__grid ul,
.activity-card__grid ol {
  margin: 0;
  padding-left: 1.05rem;
  color: var(--muted);
  font-size: 0.84rem;
  line-height: 1.55;
}

.activity-card__grid li + li {
  margin-top: 0.15rem;
}

.activity-card__safety {
  border: 1px solid #fed7aa;
  border-radius: 12px;
  background: #fff8ed;
  padding: 0.55rem 0.65rem;
}

.activity-card__safety h4 {
  color: #9a3412;
}

.observation-list {
  display: grid;
  gap: 0.4rem;
  margin: 0.75rem 0 0;
  padding-left: 1.15rem;
  color: var(--muted);
  font-size: 0.9rem;
  line-height: 1.6;
}

/* ---------- Subject page ---------- */

.subject-head {
  padding-bottom: 1.1rem;
  border-bottom: 1px solid var(--line);
  margin-bottom: 1.1rem;
}

.subject-head__title {
  display: flex;
  align-items: center;
  gap: 0.65rem;
}

.subject-head__title h1 {
  margin: 0;
  font-size: clamp(1.5rem, 3vw, 2.1rem);
  letter-spacing: -0.03em;
}

.subject-head__icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 2.35rem;
  height: 2.35rem;
  border-radius: 13px;
  background: linear-gradient(135deg, var(--brand-soft), #f1ebfe);
  font-size: 1.1rem;
}

.subject-head .lead {
  max-width: 62ch;
  margin: 0.6rem 0 0;
  color: var(--muted);
}

.subject-topics .topic-grid {
  margin-top: 0;
}

/* ---------- Age rails (0-3 / 3-5) ---------- */
.age-rails {
  display: flex;
  flex-direction: column;
  gap: 1.6rem;
  margin-top: 0.4rem;
}

.age-rail__head {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin-bottom: 0.55rem;
}

.age-rail__title {
  margin: 0;
  font-size: 1.02rem;
  letter-spacing: -0.01em;
}

.age-rail__count {
  color: var(--muted);
  font-size: 0.74rem;
  font-weight: 600;
}

.age-rail__controls {
  display: flex;
  gap: 0.35rem;
  margin-left: auto;
}

.rail-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 1.85rem;
  height: 1.85rem;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--surface);
  color: var(--ink);
  font-size: 0.95rem;
  line-height: 1;
  cursor: pointer;
  transition: border-color 0.16s ease, color 0.16s ease, background 0.16s ease;
}

.rail-btn:hover:not(:disabled) {
  border-color: var(--brand);
  color: var(--brand-strong);
  background: var(--brand-soft);
}

.rail-btn:disabled {
  opacity: 0.35;
  cursor: default;
}

.age-rail__track {
  display: flex;
  gap: 0.85rem;
  overflow-x: auto;
  padding: 0.15rem 0.15rem 0.85rem;
  scroll-snap-type: x mandatory;
  scrollbar-width: thin;
  scrollbar-color: #cbd5e1 transparent;
  overscroll-behavior-x: contain;
}

.age-rail__track > .topic-card {
  flex: 0 0 255px;
  scroll-snap-align: start;
}

.age-rail__empty {
  flex: 0 0 255px;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 8.5rem;
  padding: 1rem;
  border: 1px dashed var(--line);
  border-radius: var(--radius-lg);
  color: var(--muted);
  font-size: 0.84rem;
  text-align: center;
  background: var(--surface-soft);
}

.age-rails {
  gap: 2rem;
}

.age-group {
  display: flex;
  flex-direction: column;
  gap: 0.9rem;
}

.age-group__head {
  display: flex;
  align-items: baseline;
  gap: 0.6rem;
  margin-bottom: 0.15rem;
}

.age-group__title {
  margin: 0;
  font-size: 1.22rem;
  letter-spacing: -0.01em;
}

.age-group__count {
  color: var(--muted);
  font-size: 0.76rem;
  font-weight: 600;
}

.age-rail__track > .resource-card {
  flex: 0 0 235px;
}

.age-group__level {
  color: var(--brand-strong);
  font-size: 0.72rem;
  font-weight: 700;
}

.resource-card--media {
  padding: 0;
  overflow: hidden;
}

.resource-card__media {
  display: block;
  width: 100%;
  aspect-ratio: 4 / 3;
  object-fit: cover;
  background: var(--surface-soft);
}

.resource-card__body {
  display: flex;
  flex-direction: column;
  gap: 0.45rem;
  padding: 0.95rem 1rem 1rem;
}

.resource-card__level {
  align-self: flex-start;
  padding: 0.12rem 0.5rem;
  border-radius: 999px;
  background: var(--brand-soft);
  color: var(--brand-strong);
  font-size: 0.66rem;
  font-weight: 700;
  letter-spacing: 0.03em;
  text-transform: uppercase;
}

.resource-card__title {
  margin: 0;
  font-size: 1rem;
  line-height: 1.3;
}

.resource-card__text {
  margin: 0;
  color: var(--muted);
  font-size: 0.84rem;
  line-height: 1.45;
}

.resource-card__foot {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  margin-top: auto;
  padding-top: 0.3rem;
}

@media (max-width: 640px) {
  .age-rail__track > .topic-card,
  .age-rail__track > .resource-card,
  .age-rail__empty {
    flex-basis: 82vw;
  }
}

@media (prefers-reduced-motion: reduce) {
  .age-rail__track {
    scroll-behavior: auto;
    scroll-snap-type: none;
  }
}

.site-footer {
  margin-top: auto;
}

@media (max-width: 1024px) {
  .sidebar {
    position: fixed;
    top: 0;
    left: 0;
    width: min(82vw, 300px);
    flex-basis: auto;
    transform: translateX(-102%);
    transition: transform 200ms ease;
    box-shadow: 0 0 0 1px var(--line), 20px 0 50px rgba(15, 23, 42, 0.12);
  }

  .sidebar__close {
    display: inline-flex;
  }

  .year__summary {
    padding: 0.5rem 0.6rem;
    font-size: 0.9rem;
  }

  .subject-link {
    min-height: 2.2rem;
    padding: 0.45rem 0.55rem;
    font-size: 0.84rem;
  }

  .subject-link__icon {
    font-size: 0.82rem;
  }

  .sidebar-open .sidebar {
    transform: translateX(0);
  }

  .sidebar-backdrop {
    display: block;
    position: fixed;
    inset: 0;
    z-index: 35;
    background: rgba(15, 23, 42, 0.32);
    backdrop-filter: blur(2px);
  }

  .sidebar-backdrop[hidden] {
    display: none;
  }

  .menu-toggle {
    display: inline-flex;
  }

  .topbar {
    padding: 0 1rem;
  }
}

@media (max-width: 640px) {
  .content-inner {
    padding-inline: 1rem;
  }

  .home-hero {
    text-align: left;
  }

  .home-hero h1,
  .home-hero > p:not(.eyebrow) {
    margin-inline: 0;
  }

  .hero-search {
    flex-direction: column;
    border-radius: 18px;
    padding: 0.6rem;
  }

  .hero-search input {
    padding: 0.55rem 0.7rem;
  }

  .hero-search .btn {
    width: 100%;
  }

  .home-hero__stats {
    justify-content: flex-start;
  }

  .topic-grid {
    grid-template-columns: 1fr;
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
  }
}

@media print {
  .site-header,
  .site-footer,
  .sidebar,
  .topbar,
  .sidebar-backdrop,
  .toc,
  .prev-next,
  .btn,
  .option,
  .fill-row,
  .order-list button,
  .quiz button,
  .resources,
  .skip-link {
    display: none !important;
  }

  body {
    background: #fff;
    color: #000;
    font-size: 11pt;
  }

  .wrap {
    width: 100%;
  }

  main {
    padding: 0;
  }

  .topic-header,
  .exercise,
  .reading-text,
  .download-card,
  .multimedia-card {
    box-shadow: none;
    border-color: #bbb;
    break-inside: avoid;
  }

  h2 {
    break-after: avoid;
  }

  a {
    color: #000;
    text-decoration: underline;
  }
}