/* ============================================================
   人工智能：现代方法 · 中文学习指南
   主色：Berkeley Blue #003262 / California Gold #fdb515
   ============================================================ */
:root {
  --paper: #faf7f2;
  --card: #ffffff;
  --ink: #23262d;
  --muted: #6d7480;
  --blue: #003262;
  --blue-soft: #eef3f9;
  --blue-link: #0a4d8c;
  --gold: #fdb515;
  --gold-deep: #9a6b00;
  --green: #1a7f4e;
  --green-soft: #e9f5ee;
  --line: #e7e1d5;
  --code-bg: #f4f0e8;
  --serif: "Noto Serif SC", "Source Han Serif SC", "Songti SC", "STSong", Georgia, serif;
  --sans: -apple-system, BlinkMacSystemFont, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Segoe UI", sans-serif;
  --mono: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --shadow: 0 1px 3px rgba(35, 38, 45, .06), 0 4px 16px rgba(35, 38, 45, .05);
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.75;
  color: var(--ink);
  background: var(--paper);
}
a { color: var(--blue-link); text-decoration: none; }
a:hover { text-decoration: underline; }
img, svg { vertical-align: middle; }
.wrap { max-width: 1060px; margin: 0 auto; padding: 0 20px; }

/* ---------- 页头 ---------- */
.site-header {
  background: var(--card);
  border-bottom: 1px solid var(--line);
  position: sticky;
  top: 0;
  z-index: 50;
}
.header-inner {
  display: flex;
  align-items: center;
  gap: 20px;
  min-height: 60px;
}
.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  color: var(--blue);
  font-family: var(--serif);
  font-weight: 700;
  font-size: 17px;
  white-space: nowrap;
}
.brand:hover { text-decoration: none; }
.brand .mark {
  width: 34px; height: 34px;
  background: var(--blue);
  color: var(--gold);
  border-radius: 8px;
  display: flex; align-items: center; justify-content: center;
  font-size: 13px; letter-spacing: .5px;
  font-family: var(--serif);
}
.brand em {
  display: block;
  font-style: normal;
  font-size: 11px;
  color: var(--muted);
  font-family: var(--sans);
  font-weight: 400;
  letter-spacing: .12em;
}
.site-nav { display: flex; gap: 4px; margin-left: 8px; }
.site-nav a {
  padding: 6px 12px;
  border-radius: 6px;
  color: var(--ink);
  font-size: 14.5px;
}
.site-nav a:hover { background: var(--blue-soft); text-decoration: none; color: var(--blue); }
.site-nav a.active { color: var(--blue); font-weight: 600; }

.search { position: relative; margin-left: auto; }
.search input {
  width: 210px;
  padding: 7px 12px 7px 32px;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--paper) url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='14' height='14' viewBox='0 0 24 24' fill='none' stroke='%236d7480' stroke-width='2.4'%3E%3Ccircle cx='11' cy='11' r='7'/%3E%3Cpath d='m20 20-3.5-3.5'/%3E%3C/svg%3E") 10px center no-repeat;
  font-size: 13.5px;
  color: var(--ink);
  outline: none;
  transition: width .2s ease, border-color .2s ease;
}
.search input:focus { width: 260px; border-color: var(--blue); }
.search-results {
  position: absolute;
  top: calc(100% + 8px);
  right: 0;
  width: 340px;
  max-height: 420px;
  overflow: auto;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  box-shadow: var(--shadow);
  display: none;
}
.search-results.open { display: block; }
.search-results a {
  display: block;
  padding: 10px 14px;
  border-bottom: 1px solid #f1ede4;
  color: var(--ink);
  font-size: 14px;
  line-height: 1.5;
}
.search-results a:last-child { border-bottom: 0; }
.search-results a:hover, .search-results a.sel { background: var(--blue-soft); text-decoration: none; }
.search-results .s-cat { display: block; font-size: 11.5px; color: var(--muted); }
.search-results .s-empty { padding: 14px; color: var(--muted); font-size: 13.5px; }

/* ---------- 首页 Hero ---------- */
.hero {
  background:
    radial-gradient(1200px 400px at 85% -10%, rgba(253, 181, 21, .14), transparent 60%),
    radial-gradient(900px 380px at 0% 0%, rgba(0, 50, 98, .07), transparent 55%),
    var(--paper);
  border-bottom: 1px solid var(--line);
  padding: 64px 0 56px;
  text-align: center;
}
.hero .kicker {
  display: inline-block;
  font-size: 13px;
  letter-spacing: .35em;
  color: var(--gold-deep);
  border: 1px solid #ead9a8;
  background: #fdf6e3;
  border-radius: 999px;
  padding: 4px 14px 4px 18px;
  margin-bottom: 22px;
}
.hero h1 {
  font-family: var(--serif);
  font-size: clamp(30px, 5vw, 46px);
  line-height: 1.25;
  margin: 0 0 10px;
  color: var(--blue);
  font-weight: 900;
}
.hero .en {
  font-size: 15px;
  color: var(--muted);
  margin: 0 0 18px;
  letter-spacing: .04em;
}
.hero .desc {
  max-width: 640px;
  margin: 0 auto 28px;
  color: var(--ink);
  font-size: 16.5px;
}
.hero .desc b { color: var(--blue); }
.hero-actions { display: flex; gap: 12px; justify-content: center; flex-wrap: wrap; }
.btn {
  display: inline-block;
  padding: 10px 22px;
  border-radius: 999px;
  font-size: 15px;
  font-weight: 600;
  border: 1.5px solid var(--blue);
  transition: transform .15s ease, box-shadow .15s ease;
}
.btn:hover { text-decoration: none; transform: translateY(-1px); }
.btn-primary { background: var(--blue); color: #fff; }
.btn-primary:hover { box-shadow: 0 6px 18px rgba(0, 50, 98, .28); }
.btn-ghost { color: var(--blue); background: transparent; }
.btn-ghost:hover { background: var(--blue-soft); }

.stat-row {
  display: flex;
  justify-content: center;
  gap: clamp(20px, 6vw, 72px);
  margin-top: 40px;
  flex-wrap: wrap;
}
.stat { text-align: center; }
.stat .num {
  font-family: var(--serif);
  font-size: 32px;
  font-weight: 900;
  color: var(--blue);
  line-height: 1.1;
}
.stat .lbl { font-size: 13px; color: var(--muted); letter-spacing: .06em; }

/* 学习进度条 */
.progress-panel {
  max-width: 640px;
  margin: 34px auto 0;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 16px 20px;
  box-shadow: var(--shadow);
  display: none;
}
.progress-panel.show { display: block; }
.progress-panel .p-head {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  font-size: 14px;
  margin-bottom: 8px;
}
.progress-panel .p-head b { color: var(--blue); }
.progress-panel .p-link { font-size: 13.5px; }
.progress-bar {
  height: 8px;
  background: var(--code-bg);
  border-radius: 999px;
  overflow: hidden;
}
.progress-bar > i {
  display: block;
  height: 100%;
  width: 0;
  border-radius: 999px;
  background: linear-gradient(90deg, var(--blue), #2a6fb5);
  transition: width .4s ease;
}

/* ---------- 通用区块 ---------- */
.section { padding: 48px 0; }
.section-head { text-align: center; margin-bottom: 34px; }
.section-head h2 {
  font-family: var(--serif);
  font-size: 28px;
  color: var(--blue);
  margin: 0 0 6px;
  font-weight: 900;
}
.section-head p { color: var(--muted); margin: 0; font-size: 15px; }

/* ---------- 部分卡片 ---------- */
.parts-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 18px;
}
.part-card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 22px 22px 16px;
  position: relative;
  overflow: hidden;
  transition: box-shadow .2s ease, transform .2s ease;
}
.part-card:hover { box-shadow: var(--shadow); transform: translateY(-2px); }
.part-card .roman {
  position: absolute;
  right: 6px;
  top: -18px;
  font-family: var(--serif);
  font-size: 88px;
  font-weight: 900;
  color: rgba(0, 50, 98, .05);
  line-height: 1;
  pointer-events: none;
}
.part-card h3 {
  font-family: var(--serif);
  font-size: 19px;
  color: var(--blue);
  margin: 0 0 2px;
}
.part-card .p-en { font-size: 12.5px; color: var(--gold-deep); letter-spacing: .05em; margin-bottom: 8px; }
.part-card .p-desc { font-size: 13.5px; color: var(--muted); margin: 0 0 12px; position: relative; }
.part-card .p-meta { font-size: 12px; color: var(--muted); border-top: 1px dashed var(--line); padding-top: 10px; }
.part-card .p-meta a { color: var(--blue-link); }
.part-card .p-meta .done { color: var(--green); }
.chip-list { display: flex; flex-wrap: wrap; gap: 6px; position: relative; }
.chip {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  font-size: 12.5px;
  padding: 3px 10px;
  border-radius: 999px;
  background: var(--blue-soft);
  color: var(--blue);
  border: 1px solid #dfe8f2;
}
.chip:hover { background: var(--blue); color: #fff; text-decoration: none; }
.chip .no { font-family: var(--serif); font-weight: 700; opacity: .75; }
.chip.read { background: var(--green-soft); border-color: #cfe8da; color: var(--green); }

/* ---------- 特性条 ---------- */
.features {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 16px;
}
.feature {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 18px 20px;
}
.feature .f-ico {
  width: 38px; height: 38px;
  border-radius: 10px;
  background: var(--blue);
  color: var(--gold);
  display: flex; align-items: center; justify-content: center;
  margin-bottom: 10px;
  font-size: 17px;
}
.feature h3 { margin: 0 0 4px; font-size: 15.5px; color: var(--blue); }
.feature p { margin: 0; font-size: 13.5px; color: var(--muted); }

/* ---------- 章节页 ---------- */
.chapter-layout {
  display: grid;
  grid-template-columns: 250px minmax(0, 1fr);
  gap: 40px;
  padding: 36px 0 64px;
  align-items: start;
}
.toc {
  position: sticky;
  top: 84px;
  max-height: calc(100vh - 108px);
  overflow: auto;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 14px;
  padding: 14px 6px;
  font-size: 13px;
}
.toc .toc-toggle { display: none; }
.toc h4 {
  margin: 4px 12px 8px;
  font-size: 12px;
  letter-spacing: .18em;
  color: var(--muted);
  font-weight: 600;
}
.toc a { display: block; padding: 3px 12px; color: var(--ink); border-radius: 6px; line-height: 1.5; }
.toc a:hover { background: var(--blue-soft); text-decoration: none; }
.toc a.cur { background: var(--blue); color: #fff; }
.toc .toc-part {
  margin: 10px 12px 4px;
  font-size: 11.5px;
  color: var(--gold-deep);
  font-weight: 700;
  letter-spacing: .04em;
}
.toc a .chk { color: var(--green); margin-left: 4px; font-size: 11px; }
.toc a.cur .chk { color: var(--gold); }

.crumbs { font-size: 13px; color: var(--muted); margin-bottom: 14px; }
.crumbs a { color: var(--muted); }
.crumbs a:hover { color: var(--blue); }
.crumbs .sep { margin: 0 6px; color: #c9c2b4; }

.ch-head { border-bottom: 1px solid var(--line); padding-bottom: 18px; margin-bottom: 26px; }
.ch-head .part-badge {
  display: inline-block;
  background: var(--blue);
  color: var(--gold);
  font-size: 12px;
  border-radius: 999px;
  padding: 2px 12px;
  letter-spacing: .08em;
  margin-bottom: 10px;
  font-weight: 600;
}
.ch-head h1 {
  font-family: var(--serif);
  font-size: clamp(26px, 4vw, 36px);
  color: var(--blue);
  margin: 0 0 6px;
  font-weight: 900;
  line-height: 1.3;
}
.ch-head .en {
  color: var(--muted);
  font-size: 15px;
  margin: 0 0 12px;
}
.ch-head .ch-meta { display: flex; align-items: center; gap: 14px; flex-wrap: wrap; font-size: 13.5px; color: var(--muted); }
.ch-head .ch-meta .eta { display: inline-flex; align-items: center; gap: 6px; }

.mark-read {
  border: 1.5px solid var(--green);
  background: var(--card);
  color: var(--green);
  border-radius: 999px;
  padding: 5px 16px;
  font-size: 13.5px;
  font-weight: 600;
  cursor: pointer;
  font-family: var(--sans);
  transition: background .15s ease, color .15s ease;
}
.mark-read:hover { background: var(--green-soft); }
.mark-read.on { background: var(--green); color: #fff; }

.doc h2 {
  font-family: var(--serif);
  font-size: 21px;
  color: var(--blue);
  margin: 34px 0 12px;
  padding-left: 12px;
  border-left: 4px solid var(--gold);
  font-weight: 900;
}
.doc h2:first-child { margin-top: 0; }
.doc p { margin: 0 0 12px; }
.summary-box {
  background: var(--blue-soft);
  border: 1px solid #dfe8f2;
  border-radius: 12px;
  padding: 16px 20px;
  font-size: 15.5px;
}
ul.points { margin: 0; padding: 0; list-style: none; counter-reset: pt; }
ul.points li {
  counter-increment: pt;
  position: relative;
  padding: 0 0 14px 44px;
}
ul.points li::before {
  content: counter(pt, decimal-leading-zero);
  position: absolute;
  left: 0; top: 2px;
  width: 30px; height: 30px;
  border-radius: 8px;
  background: var(--card);
  border: 1px solid var(--line);
  color: var(--blue);
  font-family: var(--serif);
  font-size: 13px;
  font-weight: 700;
  display: flex; align-items: center; justify-content: center;
}

table.terms {
  width: 100%;
  border-collapse: collapse;
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  overflow: hidden;
  font-size: 14.5px;
}
table.terms th {
  background: var(--blue);
  color: #fff;
  text-align: left;
  padding: 9px 14px;
  font-size: 13.5px;
  letter-spacing: .05em;
  font-weight: 600;
}
table.terms td { padding: 9px 14px; border-top: 1px solid #f1ede4; vertical-align: top; }
table.terms tr:hover td { background: #fbf9f4; }
table.terms td.t-cn { white-space: nowrap; font-weight: 600; color: var(--blue); }
table.terms td.t-en { white-space: nowrap; color: var(--gold-deep); font-size: 13px; font-family: var(--mono); }
table.terms td.t-def { color: var(--ink); }

.res-list { list-style: none; margin: 0; padding: 0; display: grid; gap: 10px; }
.res-list li {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 12px 16px;
  display: flex;
  gap: 10px;
  align-items: baseline;
  font-size: 14.5px;
}
.res-list li::before { content: "▸"; color: var(--gold-deep); }
.code-list { margin: 0; padding: 0; list-style: none; display: grid; gap: 10px; }
.code-list li {
  background: var(--code-bg);
  border: 1px solid var(--line);
  border-radius: 10px;
  padding: 12px 16px;
  font-size: 14.5px;
}
.code-list code { font-family: var(--mono); font-size: 13.5px; color: var(--blue); }
.note { font-size: 13px; color: var(--muted); margin-top: 8px; }

.pager {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 12px;
  margin-top: 44px;
}
.pager a {
  border: 1px solid var(--line);
  background: var(--card);
  border-radius: 12px;
  padding: 14px 18px;
  font-size: 14px;
  color: var(--ink);
  display: block;
}
.pager a:hover { border-color: var(--blue); text-decoration: none; box-shadow: var(--shadow); }
.pager .dir { display: block; font-size: 12px; color: var(--muted); margin-bottom: 3px; letter-spacing: .1em; }
.pager .pg-title { font-weight: 600; color: var(--blue); }
.pager .next { text-align: right; }

/* ---------- 学习路径页 ---------- */
.path-card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 16px;
  padding: 26px 28px;
  margin-bottom: 22px;
  position: relative;
}
.path-card .path-no {
  position: absolute;
  right: 24px; top: 18px;
  font-family: var(--serif);
  font-size: 54px;
  font-weight: 900;
  color: rgba(253, 181, 21, .35);
  line-height: 1;
}
.path-card h2 { font-family: var(--serif); font-size: 21px; color: var(--blue); margin: 0 0 6px; }
.path-card .p-sub { color: var(--muted); font-size: 14px; margin: 0 0 14px; max-width: 560px; }
.path-card .p-tags { display: flex; gap: 8px; margin: 0 0 16px; flex-wrap: wrap; }
.path-card .p-tag {
  font-size: 12px;
  background: var(--code-bg);
  border-radius: 999px;
  padding: 2px 10px;
  color: var(--gold-deep);
}
.flow { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; }
.flow .arrow { color: #c9c2b4; font-size: 13px; }

/* ---------- 资源页 ---------- */
.res-section { margin-bottom: 34px; }
.res-section h2 {
  font-family: var(--serif);
  font-size: 20px;
  color: var(--blue);
  border-left: 4px solid var(--gold);
  padding-left: 12px;
  margin: 0 0 14px;
}
.res-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(280px, 1fr)); gap: 14px; }
.res-card {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 16px 18px;
}
.res-card h3 { margin: 0 0 4px; font-size: 15.5px; }
.res-card h3 a { color: var(--blue); }
.res-card p { margin: 0; font-size: 13.5px; color: var(--muted); }
.res-card .tag {
  display: inline-block;
  font-size: 11px;
  color: var(--gold-deep);
  background: #fdf6e3;
  border-radius: 4px;
  padding: 1px 7px;
  margin-bottom: 8px;
  letter-spacing: .05em;
}

/* ---------- 页脚 ---------- */
.site-footer {
  border-top: 1px solid var(--line);
  background: var(--card);
  padding: 28px 0 34px;
  font-size: 13px;
  color: var(--muted);
  text-align: center;
  line-height: 2;
}
.site-footer a { color: var(--blue-link); }

/* ---------- 404 ---------- */
.lost { text-align: center; padding: 100px 0; }
.lost .code { font-family: var(--serif); font-size: 90px; color: var(--blue); font-weight: 900; line-height: 1; }
.lost p { color: var(--muted); margin: 14px 0 24px; }

/* ---------- 响应式 ---------- */
@media (max-width: 920px) {
  .chapter-layout { grid-template-columns: 1fr; gap: 20px; }
  .toc { position: static; max-height: none; }
  .toc .toc-toggle {
    display: flex;
    width: 100%;
    justify-content: space-between;
    align-items: center;
    background: none;
    border: 0;
    font: inherit;
    font-weight: 700;
    color: var(--blue);
    padding: 6px 12px;
    cursor: pointer;
  }
  .toc .toc-body { display: none; padding-bottom: 6px; }
  .toc.open .toc-body { display: block; }
  .site-nav { display: none; }
  .header-inner { flex-wrap: wrap; padding-top: 8px; padding-bottom: 8px; }
  .search { width: 100%; margin: 0 0 6px; order: 3; }
  .search input, .search input:focus { width: 100%; }
  .search-results { left: 0; right: 0; width: auto; }
}
@media print {
  .site-header, .site-footer, .toc, .pager, .mark-read, .progress-panel { display: none !important; }
  body { background: #fff; }
}