:root {
  --paper: #f7f2e8;
  --ink: #1f2430;
  --muted: #5a6474;
  --line: rgba(31, 36, 48, 0.12);
  --card: rgba(255, 251, 243, 0.86);
  --accent: #c85c2b;
  --accent-soft: #f3d1bc;
  --accent-2: #0f6d69;
  --shadow: 0 18px 40px rgba(31, 36, 48, 0.08);
  --radius: 22px;
  --body-font: "Aptos", "Trebuchet MS", "Segoe UI", sans-serif;
  --title-font: "Palatino Linotype", "Book Antiqua", Georgia, serif;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

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

body {
  margin: 0;
  font-family: var(--body-font);
  color: var(--ink);
  background:
    radial-gradient(circle at top left, rgba(243, 209, 188, 0.8), transparent 32%),
    radial-gradient(circle at top right, rgba(15, 109, 105, 0.12), transparent 28%),
    linear-gradient(180deg, #fbf7ef 0%, #f5efe4 100%);
}

a {
  color: inherit;
}

.shell {
  width: min(1120px, calc(100vw - 32px));
  margin: 0 auto;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  padding: 16px 0 8px;
  backdrop-filter: blur(10px);
}

.topbar-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 18px;
  padding: 12px 18px;
  border-radius: 999px;
  background: rgba(255, 251, 243, 0.78);
  border: 1px solid rgba(255, 255, 255, 0.65);
  box-shadow: var(--shadow);
}

.brand {
  display: inline-flex;
  flex-direction: column;
  text-decoration: none;
}

.brand strong {
  font-family: var(--title-font);
  font-size: 20px;
  letter-spacing: -0.02em;
}

.brand span {
  color: var(--muted);
  font-size: 12px;
}

.nav {
  display: flex;
  flex-wrap: wrap;
  justify-content: end;
  gap: 10px;
}

.nav a {
  padding: 8px 12px;
  border-radius: 999px;
  text-decoration: none;
  color: var(--muted);
  font-size: 14px;
  font-weight: 700;
}

.nav a:hover,
.nav a.is-active {
  background: rgba(15, 109, 105, 0.1);
  color: var(--accent-2);
}

.hero {
  padding: 72px 0 40px;
}

.hero-grid {
  display: grid;
  grid-template-columns: 1.25fr 0.95fr;
  gap: 24px;
  align-items: stretch;
}

.hero-main,
.hero-side,
.card {
  background: var(--card);
  backdrop-filter: blur(12px);
  border: 1px solid rgba(255, 255, 255, 0.6);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.hero-main {
  padding: 34px 34px 30px;
}

.hero-kicker {
  display: inline-block;
  padding: 8px 14px;
  border-radius: 999px;
  background: rgba(200, 92, 43, 0.12);
  color: var(--accent);
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 0.04em;
}

.hero h1,
.page-head h1 {
  margin: 18px 0 14px;
  font-family: var(--title-font);
  font-size: clamp(40px, 6vw, 68px);
  line-height: 0.94;
  letter-spacing: -0.03em;
}

.hero p,
.page-head p {
  margin: 0;
  color: var(--muted);
  font-size: 18px;
  line-height: 1.75;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin-top: 26px;
}

.button,
.ghost {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 48px;
  padding: 0 18px;
  border-radius: 999px;
  text-decoration: none;
  font-weight: 700;
  transition: transform 0.18s ease, box-shadow 0.18s ease;
}

.button {
  background: var(--accent);
  color: #fff8f4;
  box-shadow: 0 12px 24px rgba(200, 92, 43, 0.22);
}

.ghost {
  border: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.58);
}

.button:hover,
.ghost:hover {
  transform: translateY(-2px);
}

.hero-side {
  padding: 28px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  gap: 22px;
}

.hero-side h2,
.card h2,
.section-head h2,
.page-section h2 {
  margin: 0 0 12px;
  font-family: var(--title-font);
  font-size: 28px;
  line-height: 1.1;
}

.hero-side p,
.card p,
.page-section p,
.list li,
.page-section li {
  color: var(--muted);
  line-height: 1.74;
}

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

.mini-metric .slot {
  padding: 16px 14px;
  border-radius: 18px;
  background: rgba(15, 109, 105, 0.08);
}

.slot strong {
  display: block;
  font-size: 22px;
  color: var(--accent-2);
}

.slot span {
  font-size: 13px;
  color: var(--muted);
}

.section {
  padding: 18px 0 40px;
}

.section-head {
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 18px;
}

.section-head p {
  margin: 0;
  max-width: 700px;
  color: var(--muted);
  line-height: 1.72;
}

.cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 18px;
}

.card {
  padding: 24px;
}

.card .tag {
  display: inline-block;
  margin-bottom: 14px;
  padding: 6px 12px;
  border-radius: 999px;
  background: rgba(15, 109, 105, 0.08);
  color: var(--accent-2);
  font-size: 13px;
  font-weight: 700;
}

.card ul,
.page-section ul,
.page-section ol {
  margin: 14px 0 0;
  padding-left: 20px;
}

.split {
  display: grid;
  grid-template-columns: 1.15fr 0.85fr;
  gap: 18px;
}

.rail {
  display: grid;
  gap: 18px;
}

.rail > * {
  min-width: 0;
}

.page-section code {
  overflow-wrap: anywhere;
  word-break: break-word;
}

.page {
  padding: 20px 0 44px;
}

.page-head {
  margin-bottom: 22px;
}

.crumbs {
  display: inline-flex;
  gap: 8px;
  align-items: center;
  margin-bottom: 8px;
  color: var(--muted);
  font-size: 14px;
}

.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 18px;
}

.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 18px;
}

.page-section {
  padding: 24px;
  background: var(--card);
  border: 1px solid rgba(255, 255, 255, 0.58);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.page-section h3 {
  margin: 18px 0 10px;
  font-family: var(--title-font);
  font-size: 22px;
}

.lead-list li {
  margin-bottom: 8px;
}

.roadmap-list {
  display: grid;
  gap: 14px;
}

.roadmap-item {
  padding: 18px;
  border-radius: 18px;
  background: rgba(15, 109, 105, 0.06);
  border: 1px solid rgba(15, 109, 105, 0.1);
}

.roadmap-item strong {
  display: block;
  margin-bottom: 6px;
  color: var(--accent-2);
  font-size: 18px;
}

.tiny {
  color: var(--muted);
  font-size: 14px;
}

.subject-grid {
  display: grid;
  grid-template-columns: 1.2fr 0.8fr;
  gap: 18px;
}

.subject-grid > *,
.grid-2 > *,
.grid-3 > *,
.ability-map > * {
  min-width: 0;
}

.outline-block {
  display: grid;
  gap: 12px;
}

.outline-block .node {
  padding: 16px;
  border-radius: 18px;
  background: rgba(200, 92, 43, 0.08);
}

.node strong {
  display: block;
  margin-bottom: 6px;
  color: var(--accent);
}

.learning-tree {
  display: grid;
  gap: 12px;
}

.tree-root,
.tree-node {
  display: block;
  text-decoration: none;
}

.tree-root {
  padding: 14px 16px;
  border-radius: 14px;
  background: rgba(15, 109, 105, 0.1);
  border: 1px solid rgba(15, 109, 105, 0.16);
  color: var(--accent-2);
  font-weight: 800;
}

.tree-branch {
  position: relative;
  display: grid;
  gap: 10px;
  margin-left: 10px;
  padding-left: 18px;
  border-left: 2px solid rgba(15, 109, 105, 0.18);
}

.tree-node {
  padding: 12px 14px;
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.5);
  border: 1px solid var(--line);
  font-weight: 750;
}

.tree-leaves {
  display: grid;
  gap: 8px;
  margin-left: 10px;
  padding-left: 16px;
  border-left: 1px dashed rgba(90, 100, 116, 0.38);
}

.tree-leaf {
  display: block;
  padding: 9px 12px;
  border-radius: 10px;
  color: var(--muted);
  text-decoration: none;
}

.tree-group-label {
  display: block;
  padding: 10px 12px 3px;
  color: var(--text);
  font-size: 0.82rem;
  font-weight: 800;
}

.tree-leaf:hover,
.tree-node:hover,
.tree-root:hover {
  background: rgba(200, 92, 43, 0.1);
  color: var(--accent);
}

.tree-branch.is-muted .tree-node {
  color: var(--muted);
  background: rgba(255, 255, 255, 0.32);
}

.solution-toggle {
  margin: 12px 0 18px;
  border: 1px solid rgba(15, 109, 105, 0.18);
  border-radius: 12px;
  background: rgba(15, 109, 105, 0.06);
  overflow: hidden;
}

.solution-toggle summary {
  cursor: pointer;
  padding: 11px 14px;
  color: var(--accent-2);
  font-weight: 800;
  list-style-position: inside;
}

.solution-toggle summary:hover {
  background: rgba(15, 109, 105, 0.08);
}

.solution-body {
  padding: 2px 16px 14px;
  border-top: 1px solid rgba(15, 109, 105, 0.12);
}

.solution-body > :first-child {
  margin-top: 10px;
}

.math-diagram {
  margin: 14px 0 18px;
  padding: 12px;
  border: 1px solid rgba(15, 109, 105, 0.16);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.5);
  overflow-x: auto;
}

.math-diagram svg {
  display: block;
  width: min(100%, 520px);
  height: auto;
  margin: 0 auto;
}

.audio-card {
  margin: 18px 0 22px;
  padding: 16px;
  border: 1px solid rgba(15, 109, 105, 0.16);
  border-radius: 16px;
  background: rgba(15, 109, 105, 0.06);
}

.audio-card audio {
  display: block;
  width: 100%;
}

.audio-card figcaption {
  margin-top: 10px;
  color: var(--muted);
  font-size: 14px;
  line-height: 1.55;
}

.ability-map {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  margin-top: 18px;
}

.ability-map section {
  padding: 18px;
  border: 1px solid rgba(15, 109, 105, 0.12);
  border-radius: 18px;
  background: rgba(255, 255, 255, 0.48);
}

.ability-map h3 {
  margin: 0 0 10px;
  font-size: 20px;
}

.ability-map p {
  margin: 0;
}

.footer {
  padding: 28px 0 56px;
  color: var(--muted);
  font-size: 14px;
}

.footer a {
  text-decoration: none;
  border-bottom: 1px solid rgba(90, 100, 116, 0.35);
}

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

.article h1,
.article h2,
.article h3,
.article h4 {
  font-family: var(--title-font);
  line-height: 1.18;
}

.article h1 {
  font-size: 34px;
}

.article h2 {
  margin-top: 26px;
  font-size: 28px;
}

.article h3 {
  margin-top: 22px;
  font-size: 22px;
}

.article p,
.article li,
.article blockquote,
.article code {
  line-height: 1.8;
}

.article ul,
.article ol {
  margin: 14px 0;
  padding-left: 22px;
}

.article li + li {
  margin-top: 6px;
}

.math-display {
  margin: 14px 0;
  overflow-x: auto;
}

.math-display mjx-container[jax="CHTML"][display="true"] {
  margin: 0.65em 0;
}

.article pre {
  overflow-x: auto;
  padding: 18px;
  border-radius: 18px;
  background: #1f2430;
  color: #f7f2e8;
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.08);
}

.article code {
  padding: 2px 6px;
  border-radius: 8px;
  background: rgba(15, 109, 105, 0.08);
  color: var(--accent-2);
}

.article pre code {
  padding: 0;
  background: transparent;
  color: inherit;
}

.article blockquote {
  margin: 16px 0;
  padding: 14px 18px;
  border-left: 4px solid var(--accent);
  border-radius: 0 18px 18px 0;
  background: rgba(200, 92, 43, 0.08);
}

.article hr {
  border: 0;
  border-top: 1px solid var(--line);
  margin: 28px 0;
}

.note-grid {
  display: grid;
  gap: 14px;
}

.note-item {
  padding: 16px 18px;
  border-radius: 18px;
  background: rgba(15, 109, 105, 0.06);
  border: 1px solid rgba(15, 109, 105, 0.1);
}

.note-item h3 {
  margin: 0 0 8px;
  font-size: 20px;
}

.note-item p {
  margin: 0;
}

@media (max-width: 900px) {
  .topbar-inner,
  .nav {
    display: block;
  }

  .nav {
    margin-top: 10px;
  }

  .nav a {
    display: inline-block;
    margin: 0 6px 6px 0;
  }

  .hero-grid,
  .cards,
  .split,
  .grid-2,
  .grid-3,
  .ability-map,
  .subject-grid {
    grid-template-columns: 1fr;
  }

  .hero {
    padding-top: 48px;
  }

  .mini-metric {
    grid-template-columns: 1fr;
  }
}