:root {
  --bg: #f6f4ee;
  --panel: #fffdf8;
  --panel-strong: #ffffff;
  --ink: #1d2524;
  --muted: #63706d;
  --line: #deddd5;
  --accent: #087d72;
  --accent-deep: #08665e;
  --accent-soft: #ddf3ee;
  --blue-soft: #e7efff;
  --code: #182221;
  --code-ink: #edf7f5;
  --warn: #a44717;
  --shadow: 0 14px 36px rgba(37, 50, 47, .08);
  --shadow-hover: 0 18px 44px rgba(28, 58, 52, .13);
  --radius: 20px;
  --reading-size: 17px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  min-width: 320px;
  background:
    radial-gradient(circle at 80% -10%, rgba(79, 195, 181, .14), transparent 28rem),
    radial-gradient(circle at 38% 35%, rgba(255, 255, 255, .72), transparent 34rem),
    var(--bg);
  color: var(--ink);
  font-family: -apple-system, BlinkMacSystemFont, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  line-height: 1.75;
}
button, input, textarea { font: inherit; }
button, a { -webkit-tap-highlight-color: transparent; }
a { color: var(--accent-deep); text-underline-offset: 3px; }
a:hover { color: var(--accent); }
button { touch-action: manipulation; }
button:focus-visible, a:focus-visible, input:focus-visible, textarea:focus-visible, summary:focus-visible {
  outline: 3px solid color-mix(in srgb, var(--accent) 42%, transparent);
  outline-offset: 3px;
}
code, pre, textarea {
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", Menlo, monospace;
}

.skip-link {
  position: fixed; left: 16px; top: -80px; z-index: 1000;
  padding: 10px 14px; border-radius: 8px; background: var(--ink); color: white;
}
.skip-link:focus { top: 16px; }
.app-shell { min-height: 100vh; min-height: 100dvh; }
.sidebar {
  position: fixed; inset: 0 auto 0 0; z-index: 20;
  width: 316px; overflow-y: auto; padding: 24px 18px max(24px, env(safe-area-inset-bottom));
  background: color-mix(in srgb, var(--panel) 96%, transparent); border-right: 1px solid var(--line);
  box-shadow: 8px 0 34px rgba(41, 55, 52, .045);
  scrollbar-width: thin; scrollbar-color: var(--line) transparent;
}
.page { min-height: 100vh; min-height: 100dvh; margin-left: 316px; }
.brand { display: flex; align-items: center; justify-content: space-between; margin-bottom: 20px; }
.brand-home {
  display: flex; gap: 12px; align-items: center; padding: 0; border: 0;
  color: var(--ink); background: transparent; text-align: left; cursor: pointer;
}
.brand-home strong, .brand-home small { display: block; }
.brand-home strong { font-size: 17px; }
.brand-home small { color: var(--muted); font-size: 12px; }
.brand-mark {
  display: grid; flex: 0 0 auto; place-items: center; width: 50px; height: 50px; border-radius: 15px;
  background: var(--accent); color: white; font: 700 22px Georgia, serif;
  box-shadow: 0 8px 20px rgba(15, 118, 110, .22);
}
.brand-mark sub { font-size: 10px; }
.search-box {
  display: flex; gap: 8px; align-items: center; min-height: 46px; padding: 9px 12px;
  border: 1px solid var(--line); border-radius: 12px; background: var(--panel-strong);
}
.search-box:focus-within { border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-soft); }
.search-box input { min-width: 0; width: 100%; border: 0; outline: 0; color: var(--ink); background: transparent; }
.progress-card { margin: 14px 0 12px; padding: 13px; border: 1px solid color-mix(in srgb, var(--accent) 10%, transparent); border-radius: 14px; background: var(--accent-soft); }
.progress-card > div:first-child { display: flex; justify-content: space-between; font-size: 13px; }
.progress-track { height: 7px; margin-top: 8px; overflow: hidden; border-radius: 999px; background: rgba(15, 118, 110, .16); }
.progress-track span { display: block; width: 0; height: 100%; border-radius: inherit; background: var(--accent); transition: width .25s ease; }
.lesson-nav { display: grid; gap: 4px; }
.nav-group-label { margin: 14px 8px 5px; color: var(--muted); font-size: 12px; font-weight: 700; letter-spacing: .08em; }
.lesson-link {
  display: grid; grid-template-columns: 28px 1fr 18px; gap: 8px; align-items: center;
  width: 100%; min-height: 42px; padding: 8px 9px; border: 0; border-radius: 11px;
  color: var(--ink); background: transparent; text-align: left; cursor: pointer;
}
.lesson-link:hover { background: var(--accent-soft); transform: translateX(2px); }
.lesson-link.active { background: var(--accent); color: white; }
.lesson-link .number { color: var(--muted); font-size: 12px; font-variant-numeric: tabular-nums; }
.lesson-link.active .number { color: #d8fffa; }
.lesson-link .title { overflow: hidden; text-overflow: ellipsis; white-space: nowrap; font-size: 14px; }
.lesson-link .done { color: var(--accent); font-weight: 900; }
.lesson-link.active .done { color: white; }
.sidebar-footer { display: grid; gap: 6px; margin-top: 20px; padding: 16px 8px; border-top: 1px solid var(--line); font-size: 13px; }
.topbar {
  position: sticky; top: 0; z-index: 10; display: flex; justify-content: space-between; align-items: center;
  min-height: 66px; padding: 0 34px; background: color-mix(in srgb, var(--bg) 84%, transparent);
  border-bottom: 1px solid var(--line); backdrop-filter: blur(16px);
}
.breadcrumb { color: var(--muted); font-size: 14px; }
.topbar-actions { display: flex; gap: 8px; }
.icon-button, .text-button {
  border: 1px solid var(--line); border-radius: 10px; background: var(--panel-strong); color: var(--ink); cursor: pointer;
  box-shadow: 0 4px 14px rgba(33, 47, 44, .05);
}
.icon-button:hover, .text-button:hover { border-color: color-mix(in srgb, var(--accent) 45%, var(--line)); background: var(--accent-soft); }
.icon-button { width: 40px; height: 40px; }
.text-button { padding: 6px 10px; font-size: 13px; }
.mobile-only { display: none; }
#main-content { position: relative; max-width: 1080px; margin: 0 auto; padding: 52px 54px 88px; font-size: var(--reading-size); }
.hero { padding: 10px 0 26px; }
.eyebrow { margin: 0 0 10px; color: var(--accent-deep); font-size: 13px; font-weight: 800; letter-spacing: .1em; text-transform: uppercase; }
h1, h2, h3 { color: var(--ink); line-height: 1.28; }
h1 { max-width: 840px; margin: 0; font-size: clamp(42px, 3.8vw, 58px); letter-spacing: -.038em; text-wrap: balance; }
h2 { margin: 44px 0 16px; font-size: 29px; letter-spacing: -.02em; }
h3 { margin: 30px 0 10px; font-size: 21px; }
.lead { max-width: 800px; color: var(--muted); font-size: 20px; line-height: 1.7; text-wrap: pretty; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 24px; }
.primary-button, .secondary-button, .complete-button {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  min-height: 46px; padding: 9px 17px; border-radius: 12px; font-weight: 750; text-decoration: none; cursor: pointer;
  transition: transform .16s ease, box-shadow .16s ease, background .16s ease, border-color .16s ease;
}
.primary-button { border: 1px solid var(--accent); background: var(--accent); color: white; }
.primary-button:hover { background: var(--accent-deep); color: white; box-shadow: 0 9px 22px rgba(8, 125, 114, .22); transform: translateY(-1px); }
.secondary-button { border: 1px solid var(--line); background: var(--panel-strong); color: var(--ink); }
.secondary-button:hover, .complete-button:hover { border-color: color-mix(in srgb, var(--accent) 42%, var(--line)); color: var(--accent-deep); transform: translateY(-1px); }
.complete-button { border: 1px solid var(--accent); background: var(--panel-strong); color: var(--accent-deep); }
.complete-button.done { background: var(--accent-soft); }
.feature-grid, .lesson-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 16px; }
.feature-card, .lesson-card, .content-card, .practice-card, .callout {
  border: 1px solid var(--line); border-radius: var(--radius); background: var(--panel); box-shadow: var(--shadow);
}
.feature-card { padding: 22px; transition: transform .18s ease, box-shadow .18s ease, border-color .18s ease; }
.feature-card h3 { margin-top: 0; }
.feature-card:hover { transform: translateY(-2px); border-color: color-mix(in srgb, var(--accent) 28%, var(--line)); box-shadow: var(--shadow-hover); }
.lesson-card { position: relative; padding: 20px; cursor: pointer; transition: transform .15s ease, border-color .15s ease; }
.lesson-card:hover { transform: translateY(-3px); border-color: var(--accent); box-shadow: var(--shadow-hover); }
.lesson-card .lesson-number { color: var(--accent-deep); font-size: 12px; font-weight: 800; }
.lesson-card h3 { margin: 5px 0 7px; }
.lesson-card p { margin: 0; color: var(--muted); font-size: 14px; }
.lesson-card .check { position: absolute; right: 16px; top: 15px; color: var(--accent); }
.content-card { margin: 18px 0; padding: 24px; }
.content-card > :first-child { margin-top: 0; }
.content-card > :last-child { margin-bottom: 0; }
.callout { margin: 20px 0; padding: 18px 20px; border-left: 5px solid var(--accent); box-shadow: none; }
.callout strong { color: var(--accent-deep); }
.callout.warning { border-left-color: var(--warn); background: #fff5ec; }
.callout.success { background: #e9f8ee; }
.step-list { counter-reset: steps; display: grid; gap: 16px; padding: 0; list-style: none; }
.step-list > li { position: relative; padding-left: 50px; }
.step-list > li::before {
  counter-increment: steps; content: counter(steps); position: absolute; left: 0; top: 1px;
  display: grid; place-items: center; width: 34px; height: 34px; border-radius: 50%;
  background: var(--accent-soft); color: var(--accent-deep); font-weight: 850;
}
.code-card { margin: 16px 0 22px; overflow: hidden; border: 1px solid #334341; border-radius: 15px; background: var(--code); box-shadow: 0 12px 28px rgba(16, 27, 25, .12); }
.code-toolbar { display: flex; justify-content: space-between; align-items: center; padding: 8px 12px; color: #bcd0cc; background: #111a19; font-size: 12px; }
.copy-button { min-height: 34px; padding: 5px 10px; border: 1px solid #49635f; border-radius: 8px; background: transparent; color: #eef8f6; cursor: pointer; }
.copy-button:hover { background: rgba(255, 255, 255, .08); }
.code-card pre { margin: 0; padding: 18px; overflow-x: auto; color: var(--code-ink); font-size: 14px; line-height: 1.65; tab-size: 4; }
.inline-code { padding: .1em .35em; border-radius: 5px; background: var(--accent-soft); color: var(--accent-deep); font-size: .92em; }
.explain-list { margin: 12px 0; padding-left: 22px; }
.explain-list li { margin: 6px 0; }
.practice-card { margin-top: 38px; overflow: hidden; border-color: color-mix(in srgb, var(--accent) 22%, var(--line)); }
.practice-head { padding: 20px 22px; background: linear-gradient(135deg, var(--blue-soft), var(--accent-soft)); }
.practice-head h2 { margin: 0 0 3px; font-size: 24px; }
.practice-head p { margin: 0; color: var(--muted); font-size: 14px; }
.practice-body { padding: 20px; }
.practice-editor {
  display: block; width: 100%; min-height: 260px; resize: vertical; padding: 16px;
  border: 1px solid var(--line); border-radius: 12px; outline: 0; background: var(--code); color: var(--code-ink);
  line-height: 1.55; font-size: 14px;
}
.practice-editor:focus { border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-soft); }
.practice-actions { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 12px; }
.preview-panel { margin-top: 14px; padding: 18px; border: 1px dashed var(--line); border-radius: 12px; background: white; color: #202525; }
.preview-panel[hidden] { display: none; }
.preview-panel .mock-section { margin: 16px 0 8px; font-size: 22px; font-weight: 800; }
.preview-panel .mock-subsection { margin: 14px 0 6px; font-size: 18px; font-weight: 750; }
.preview-panel .mock-math { display: inline-block; padding: 0 4px; font: italic 1.05em Georgia, serif; }
.preview-note { color: var(--muted); font-size: 12px; }
.texlive-output { margin-top: 18px; overflow: hidden; border: 1px solid var(--line); border-radius: 14px; background: var(--panel-strong); }
.texlive-output[hidden] { display: none; }
.texlive-output-head { display: flex; justify-content: space-between; gap: 12px; align-items: center; padding: 12px 14px; border-bottom: 1px solid var(--line); background: var(--accent-soft); }
.texlive-output-head strong, .texlive-output-head span { display: block; }
.texlive-output-head span { color: var(--muted); font-size: 12px; }
.texlive-output iframe { display: block; width: 100%; height: min(74vh, 760px); min-height: 560px; border: 0; background: white; }
details { margin: 16px 0; padding: 14px 16px; border: 1px solid var(--line); border-radius: 12px; background: var(--panel); }
summary { font-weight: 800; cursor: pointer; }
.screenshot { display: block; max-width: 100%; margin: 18px auto; border: 1px solid var(--line); border-radius: 14px; box-shadow: var(--shadow); }
.screenshot-caption { margin-top: -10px; color: var(--muted); text-align: center; font-size: 13px; }
.mini-table { width: 100%; border-collapse: collapse; margin: 16px 0; font-size: 15px; }
.mini-table th, .mini-table td { padding: 10px; border-bottom: 1px solid var(--line); text-align: left; vertical-align: top; }
.mini-table th { color: var(--accent-deep); }
.lesson-footer { display: flex; justify-content: space-between; gap: 14px; margin-top: 50px; padding-top: 22px; border-top: 1px solid var(--line); }
.lesson-footer button { max-width: 48%; }
.site-footer { padding: 24px 32px 40px; color: var(--muted); text-align: center; font-size: 13px; }
.toast {
  position: fixed; right: 24px; bottom: 24px; z-index: 100;
  padding: 10px 15px; border-radius: 10px; background: var(--ink); color: white;
  opacity: 0; pointer-events: none; transform: translateY(8px); transition: .2s ease;
}
.toast.show { opacity: 1; transform: translateY(0); }
.empty-search { padding: 30px 10px; color: var(--muted); text-align: center; }
.sidebar-backdrop { display: none; position: fixed; inset: 0; z-index: 30; padding: 0; border: 0; background: rgba(13, 23, 21, .46); backdrop-filter: blur(3px); }

body.large-type { --reading-size: 19px; }
body.dark {
  --bg: #111817; --panel: #18211f; --panel-strong: #202b29; --ink: #edf4f2; --muted: #a8b7b3;
  --line: #33423f; --accent: #4fc3b5; --accent-deep: #80dacc; --accent-soft: #203c37;
  --blue-soft: #1d3043; --shadow: 0 14px 38px rgba(0, 0, 0, .22);
}
body.dark .callout.warning { background: #38271e; }
body.dark .callout.success { background: #183126; }
body.dark .preview-panel { background: #fdfdf9; }

@media (min-width: 901px) and (max-width: 1180px) {
  .sidebar { width: 292px; }
  .page { margin-left: 292px; }
  #main-content { padding-inline: 38px; }
  h1 { font-size: clamp(40px, 4.6vw, 54px); }
}

@media (max-width: 900px) {
  .mobile-only { display: inline-grid; place-items: center; }
  .sidebar {
    z-index: 40; width: min(88vw, 360px); height: 100vh; height: 100dvh;
    transform: translateX(-104%); transition: transform .22s ease; box-shadow: var(--shadow-hover);
  }
  body.sidebar-open .sidebar { transform: translateX(0); }
  body.sidebar-open { overflow: hidden; }
  body.sidebar-open .sidebar-backdrop { display: block; }
  .page { margin-left: 0; }
  .topbar { min-height: 62px; padding: 0 max(16px, env(safe-area-inset-right)) 0 max(16px, env(safe-area-inset-left)); }
  .breadcrumb { max-width: min(54vw, 420px); overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
  #main-content { padding: 36px max(20px, env(safe-area-inset-right)) 68px max(20px, env(safe-area-inset-left)); }
  .feature-grid, .lesson-grid { grid-template-columns: 1fr; }
  .topbar-actions { margin-left: auto; }
  .sidebar-backdrop { cursor: default; }
}

@media (max-width: 620px) {
  .topbar { gap: 9px; }
  .breadcrumb { max-width: calc(100vw - 196px); font-size: 12px; }
  .topbar-actions { gap: 6px; }
  .text-button { min-height: 40px; padding-inline: 9px; }
  #main-content { padding-top: 28px; }
  .hero { padding-top: 4px; }
  h1 { font-size: clamp(34px, 10.5vw, 44px); letter-spacing: -.04em; }
  h2 { margin-top: 38px; font-size: 26px; }
  h3 { font-size: 20px; }
  .lead { font-size: 18px; line-height: 1.65; }
  .hero-actions { display: grid; grid-template-columns: 1fr; }
  .hero-actions > * { width: 100%; }
  .feature-card, .lesson-card { padding: 18px; }
  .content-card { padding: 18px; }
  .callout { padding: 16px; }
  .code-card { margin-inline: -2px; border-radius: 13px; }
  .code-toolbar { padding: 8px 10px; }
  .code-card pre { padding: 14px; font-size: 12.5px; line-height: 1.62; -webkit-overflow-scrolling: touch; }
  .practice-head { padding: 18px; }
  .practice-body { padding: 14px; }
  .practice-editor { min-height: 300px; padding: 14px; font-size: 13px; }
  .practice-actions { display: grid; grid-template-columns: 1fr 1fr; }
  .practice-actions > :first-child { grid-column: 1 / -1; }
  .practice-actions button { min-width: 0; padding-inline: 10px; }
  .mini-table { display: block; max-width: 100%; overflow-x: auto; -webkit-overflow-scrolling: touch; }
  .mini-table th, .mini-table td { min-width: 110px; }
  .screenshot { border-radius: 11px; }
  .lesson-footer { flex-direction: column; }
  .lesson-footer button { max-width: none; width: 100%; }
  .texlive-output-head { align-items: flex-start; padding: 10px 12px; }
  .texlive-output-head .text-button { flex: 0 0 auto; }
  .texlive-output iframe { height: calc(100dvh - 150px); min-height: 480px; }
  .toast { right: 16px; bottom: max(16px, env(safe-area-inset-bottom)); left: 16px; text-align: center; }
}

@media (max-width: 390px) {
  .brand-home small { display: none; }
  .practice-actions { grid-template-columns: 1fr; }
  .practice-actions > :first-child { grid-column: auto; }
}

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

@media print {
  .sidebar, .sidebar-backdrop, .topbar, .site-footer, .lesson-footer, .practice-actions, .copy-button { display: none !important; }
  .page { margin: 0; }
  #main-content { max-width: none; padding: 0; }
  .content-card, .practice-card { box-shadow: none; break-inside: avoid; }
}