:root {
  --bg: #f7f3eb;
  --surface: #fffdf8;
  --surface-2: #eeeae0;
  --surface-3: #e7efeb;
  --ink: #17201c;
  --muted: #5f6d68;
  --line: #d8d0c3;
  --accent: #0f6655;
  --accent-2: #315c96;
  --accent-3: #8b5a20;
  --code-bg: #111918;
  --code-fg: #e8f4ef;
  --content: 1120px;
  color: var(--ink);
  background: var(--bg);
}

[data-theme="dark"] {
  --bg: #111514;
  --surface: #171d1b;
  --surface-2: #202722;
  --surface-3: #162823;
  --ink: #e9efeb;
  --muted: #9da8a3;
  --line: #33403a;
  --accent: #73d2bc;
  --accent-2: #94b8ff;
  --accent-3: #e1a75d;
  --code-bg: #090d0c;
  --code-fg: #dff0ea;
}

* { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: 78px;
}

body {
  min-width: 320px;
  margin: 0;
  overflow-x: hidden;
  background: var(--bg);
  color: var(--ink);
  font-family: ui-sans-serif, -apple-system, BlinkMacSystemFont, "SF Pro Text", "PingFang SC", "Microsoft YaHei", sans-serif;
  font-size: 17px;
  line-height: 1.76;
  text-rendering: optimizeLegibility;
}

button { font: inherit; }

a {
  color: var(--accent);
  text-underline-offset: 3px;
}

#progress {
  position: fixed;
  inset: 0 auto auto 0;
  z-index: 100;
  width: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 50;
  display: flex;
  align-items: center;
  gap: 12px;
  min-height: 58px;
  padding: 8px max(14px, env(safe-area-inset-left));
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--surface) 92%, transparent);
  backdrop-filter: blur(14px);
}

.topbar-title {
  flex: 1;
  overflow: hidden;
  color: var(--ink);
  font-size: 15px;
  font-weight: 780;
  white-space: nowrap;
  text-overflow: ellipsis;
}

.icon-button {
  display: inline-grid;
  place-items: center;
  min-width: 40px;
  min-height: 40px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--ink);
  cursor: pointer;
  text-decoration: none;
}

.layout {
  display: grid;
  grid-template-columns: 318px minmax(0, 1fr);
  min-height: calc(100vh - 58px);
}

.sidebar {
  position: sticky;
  top: 58px;
  height: calc(100vh - 58px);
  overflow-y: auto;
  padding: 24px 18px 40px max(20px, env(safe-area-inset-left));
  border-right: 1px solid var(--line);
}

.sidebar-label {
  margin: 0 0 12px;
  color: var(--muted);
  font-size: 12px;
  font-weight: 820;
  letter-spacing: .12em;
  text-transform: uppercase;
}

#side-nav a {
  display: block;
  padding: 7px 10px;
  border-radius: 8px;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.38;
  text-decoration: none;
}

#side-nav a:hover,
#side-nav a.active {
  color: var(--accent);
  background: var(--surface-3);
}

#side-nav a.sub {
  padding-left: 23px;
  font-size: 12px;
}

main {
  min-width: 0;
  padding: 54px 30px 100px;
}

article {
  width: min(100%, var(--content));
  margin: 0 auto;
  overflow-wrap: anywhere;
}

.kicker {
  margin: 0 0 12px;
  color: var(--accent);
  font-size: 12px;
  font-weight: 850;
  letter-spacing: .13em;
  text-transform: uppercase;
}

h1, h2, h3, h4 {
  line-height: 1.32;
  letter-spacing: 0;
}

h1 {
  margin: 0;
  max-width: 18ch;
  font: 760 clamp(2.25rem, 5vw, 4.4rem) / 1.08 ui-serif, "Songti SC", STSong, Georgia, serif;
}

h2 {
  margin: 82px 0 26px;
  padding-top: 34px;
  border-top: 1px solid var(--line);
  font-size: clamp(1.6rem, 4vw, 2.25rem);
}

h3 {
  margin: 34px 0 14px;
  font-size: 1.23rem;
}

h4 {
  margin: 22px 0 10px;
  font-size: 1.05rem;
}

p, ul, ol, table, pre, .diagram, .lesson-card, .assignment-card, .module-card, .callout {
  margin-top: 0;
  margin-bottom: 24px;
}

ul, ol { padding-left: 1.45em; }
li + li { margin-top: 7px; }

code {
  padding: .16em .38em;
  border: 1px solid var(--line);
  border-radius: 5px;
  background: var(--surface-2);
  color: var(--ink);
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
  font-size: .88em;
}

table {
  display: block;
  width: 100%;
  overflow-x: auto;
  border-collapse: collapse;
  border-spacing: 0;
  font-size: 14px;
  line-height: 1.55;
}

th, td {
  min-width: 126px;
  padding: 11px 13px;
  border: 1px solid var(--line);
  text-align: left;
  vertical-align: top;
}

th { background: var(--surface-2); }

.lede {
  max-width: 70ch;
  margin: 24px 0 0;
  color: var(--muted);
  font-size: 1.06rem;
}

.hero-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  margin: 34px 0 8px;
}

.stat {
  min-height: 112px;
  padding: 18px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
}

.stat strong {
  display: block;
  color: var(--accent);
  font: 760 1.95rem / 1.1 ui-serif, "Songti SC", STSong, Georgia, serif;
}

.stat span {
  display: block;
  margin-top: 8px;
  color: var(--muted);
  font-size: 14px;
  line-height: 1.5;
}

.callout {
  padding: 18px 20px;
  border: 1px solid color-mix(in srgb, var(--accent) 38%, var(--line));
  border-radius: 8px;
  background: var(--surface-3);
}

.callout strong { color: var(--accent); }

.warning {
  border-color: color-mix(in srgb, var(--accent-3) 42%, var(--line));
  background: color-mix(in srgb, var(--surface) 78%, var(--accent-3) 11%);
}

.chapter {
  scroll-margin-top: 78px;
  margin-top: 52px;
  padding-top: 30px;
  border-top: 1px solid var(--line);
}

.chapter h3 {
  margin-top: 0;
  font-size: clamp(1.28rem, 3vw, 1.65rem);
}

.chapter h4 { color: var(--accent); }

.chapter-lede {
  color: var(--muted);
  font-size: 1.03rem;
}

.concept-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin: 22px 0 26px;
}

.concept-card {
  min-height: 118px;
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface-2);
}

.concept-card strong {
  display: block;
  color: var(--accent);
  line-height: 1.35;
}

.concept-card span {
  display: block;
  margin-top: 7px;
  color: var(--muted);
  font-size: 14px;
  line-height: 1.58;
}

.formula {
  margin: 18px 0 24px;
  padding: 16px 18px;
  overflow-x: auto;
  border-radius: 8px;
  background: var(--code-bg);
  color: var(--code-fg);
  font-family: "SFMono-Regular", Consolas, "Liberation Mono", monospace;
  font-size: 14px;
  line-height: 1.62;
  white-space: pre-wrap;
}

pre {
  padding: 16px 18px;
  overflow-x: auto;
  border-radius: 8px;
  background: var(--code-bg);
  color: var(--code-fg);
}

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

.reader-check {
  margin: 22px 0 26px;
  padding: 14px 16px;
  border: 1px dashed color-mix(in srgb, var(--accent) 45%, var(--line));
  border-radius: 8px;
  background: color-mix(in srgb, var(--surface) 84%, var(--accent) 6%);
}

.reader-check summary {
  cursor: pointer;
  color: var(--accent);
  font-weight: 760;
}

.reader-check p:last-child { margin-bottom: 0; }

.chapter table strong { color: var(--accent); }

.chapter-index {
  margin: 24px 0 34px;
  padding: 16px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface-2);
}

.chapter-index-title {
  margin-bottom: 12px;
  color: var(--accent);
  font-size: 13px;
  font-weight: 820;
}

.chapter-index-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px 12px;
}

.chapter-index a {
  display: block;
  padding: 8px 10px;
  border: 1px solid color-mix(in srgb, var(--line) 72%, transparent);
  border-radius: 8px;
  background: var(--surface);
  color: var(--ink);
  font-size: 13px;
  line-height: 1.4;
  text-decoration: none;
}

.chapter-index a:hover {
  color: var(--accent);
  border-color: color-mix(in srgb, var(--accent) 42%, var(--line));
}

.diagram {
  padding: 16px;
  overflow-x: auto;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface-2);
}

.pipeline {
  display: grid;
  grid-template-columns: repeat(var(--pipeline-columns, 6), minmax(134px, 1fr));
  gap: 10px;
  min-width: var(--pipeline-min, 860px);
}

.node {
  position: relative;
  min-height: 116px;
  padding: 14px;
  border: 1px solid color-mix(in srgb, var(--accent) 30%, var(--line));
  border-radius: 8px;
  background: var(--surface);
}

.node::after {
  content: "→";
  position: absolute;
  top: 42px;
  right: -16px;
  color: var(--accent-2);
  font-weight: 800;
}

.node:last-child::after { content: ""; }

.node strong {
  display: block;
  margin-bottom: 6px;
  color: var(--accent);
  line-height: 1.35;
}

.node span {
  display: block;
  color: var(--muted);
  font-size: 13px;
  line-height: 1.5;
}

.module-grid,
.assignment-grid,
.glossary {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 14px;
}

.module-card,
.assignment-card,
.lesson-card {
  padding: 20px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: color-mix(in srgb, var(--surface) 88%, var(--surface-2));
}

.module-card h3,
.assignment-card h3,
.lesson-card h3 { margin-top: 0; }

.tag-row {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin: 12px 0 16px;
}

.tag {
  display: inline-flex;
  align-items: center;
  min-height: 28px;
  padding: 3px 9px;
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--muted);
  background: var(--surface);
  font-size: 12px;
  line-height: 1.35;
}

.tag.accent {
  color: var(--accent);
  border-color: color-mix(in srgb, var(--accent) 40%, var(--line));
}

.lesson-card { scroll-margin-top: 78px; }

.lesson-head {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr);
  gap: 16px;
  align-items: start;
}

.lesson-num {
  display: grid;
  place-items: center;
  width: 48px;
  height: 48px;
  border-radius: 8px;
  background: var(--accent);
  color: var(--surface);
  font-weight: 850;
  line-height: 1;
}

.lesson-meta {
  color: var(--muted);
  font-size: 13px;
  line-height: 1.45;
}

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

.mini {
  padding: 14px 15px;
  border-left: 3px solid var(--accent-2);
  border-radius: 0 8px 8px 0;
  background: var(--surface-2);
}

.mini h4 {
  margin-top: 0;
  color: var(--accent-2);
}

.exercise {
  padding: 15px;
  border: 1px dashed color-mix(in srgb, var(--accent) 45%, var(--line));
  border-radius: 8px;
  background: color-mix(in srgb, var(--surface) 84%, var(--accent) 6%);
}

.exercise p:last-child { margin-bottom: 0; }

.reveal {
  margin-top: 10px;
  padding: 7px 11px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface);
  color: var(--accent);
  cursor: pointer;
}

.answer {
  display: none;
  margin-top: 12px;
  color: var(--muted);
  font-size: 14px;
}

.answer.open { display: block; }

.progress-box {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  margin-top: 16px;
  color: var(--muted);
  font-size: 13px;
}

.progress-box input {
  width: 18px;
  height: 18px;
  margin-top: 4px;
  accent-color: var(--accent);
}

.source-list a,
.link-row a {
  display: inline-block;
  margin: 0 10px 10px 0;
}

.term {
  padding: 14px 15px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface-2);
}

.term strong {
  display: block;
  color: var(--accent);
}

.term span {
  display: block;
  margin-top: 5px;
  color: var(--muted);
  font-size: 14px;
  line-height: 1.58;
}

.meta {
  width: min(100%, var(--content));
  margin: 18px auto 0;
  color: var(--muted);
  font-size: 12px;
  text-align: right;
}

#back-top {
  position: fixed;
  right: max(18px, env(safe-area-inset-right));
  bottom: max(18px, env(safe-area-inset-bottom));
  z-index: 30;
  display: none;
}

.scrim { display: none; }

@media (min-width: 1121px) {
  #menu { display: none; }
}

@media (max-width: 1120px) {
  .layout { display: block; }

  .sidebar {
    position: fixed;
    inset: 0 auto 0 0;
    z-index: 70;
    width: min(84vw, 340px);
    height: 100vh;
    padding-top: 76px;
    transform: translateX(-105%);
    transition: transform .2s ease;
    background: var(--surface);
  }

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

  .scrim {
    position: fixed;
    inset: 0;
    left: min(84vw, 340px);
    z-index: 60;
    background: rgba(0, 0, 0, .38);
  }

  body.nav-open .scrim { display: block; }

  main { padding: 22px 12px 88px; }
  h2 { margin-top: 66px; }
  .meta { padding: 0 8px; }
}

@media (max-width: 780px) {
  body {
    font-size: 16px;
    line-height: 1.74;
  }

  h1 { font-size: 2.05rem; }
  h2 { font-size: 1.55rem; }
  h3 { font-size: 1.18rem; }

  .hero-grid,
  .module-grid,
  .two-col,
  .concept-grid,
  .chapter-index-grid,
  .assignment-grid,
  .glossary {
    grid-template-columns: 1fr;
  }

  .lesson-head {
    grid-template-columns: 1fr;
    gap: 10px;
  }

  .lesson-num {
    width: 42px;
    height: 42px;
  }

  th, td {
    min-width: 145px;
    padding: 9px 10px;
  }
}

@media (prefers-reduced-motion: reduce) {
  * { transition: none !important; scroll-behavior: auto !important; }
}

@media print {
  .topbar,
  .sidebar,
  #progress,
  #back-top,
  .scrim,
  .reveal,
  .progress-box {
    display: none !important;
  }

  .layout { display: block; }
  main { padding: 0; }
  article { width: 100%; max-width: none; }
  h2 { break-before: page; }
  a { color: inherit; }
  .answer { display: block; }
}