/* ============================================================
   学科地图 × 深度学习 —— 教学网站全局样式
   设计语言：深色科技风 · 青→蓝渐变 · 大留白 · SVG 图解为主
   ============================================================ */

:root {
  --bg: #0a0e1a;
  --bg-soft: #0d1322;
  --card: #111a2e;
  --card-2: #16223c;
  --card-3: #1b2a4a;
  --border: #223153;
  --border-2: #2e4068;
  --text: #e8eef9;
  --text-dim: #a9b6cd;
  --text-muted: #6d7d99;
  --teal: #00d4aa;
  --blue: #38a3ff;
  --purple: #8b5cf6;
  --pink: #ec4899;
  --orange: #f5a623;
  --red: #f5576c;
  --green: #4ade80;
  --yellow: #facc15;
  --grad: linear-gradient(135deg, #00d4aa 0%, #38a3ff 100%);
  --grad-2: linear-gradient(135deg, #8b5cf6 0%, #ec4899 100%);
  --grad-3: linear-gradient(135deg, #f5a623 0%, #f5576c 100%);
  --shadow: 0 10px 40px rgba(0, 0, 0, 0.45);
  --shadow-sm: 0 4px 16px rgba(0, 0, 0, 0.35);
  --radius: 14px;
  --radius-lg: 22px;
  --font: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei",
    "Noto Sans SC", "Source Han Sans SC", system-ui, sans-serif;
  --mono: "Cascadia Code", "JetBrains Mono", Consolas, "Courier New", monospace;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.75;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

/* ---------- 滚动条 ---------- */
::-webkit-scrollbar { width: 10px; height: 10px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--border-2); border-radius: 8px; }
::-webkit-scrollbar-thumb:hover { background: #3d5385; }

/* ---------- 顶部导航 ---------- */
.topbar {
  position: fixed;
  inset: 0 0 auto 0;
  z-index: 100;
  display: flex;
  align-items: center;
  gap: 18px;
  padding: 0 28px;
  height: 60px;
  background: rgba(10, 14, 26, 0.82);
  backdrop-filter: blur(14px);
  border-bottom: 1px solid var(--border);
}

.brand {
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 800;
  font-size: 17px;
  color: var(--text);
  text-decoration: none;
  white-space: nowrap;
}
.brand .logo-dot {
  width: 26px; height: 26px;
  border-radius: 8px;
  background: var(--grad);
  display: grid; place-items: center;
  font-size: 14px;
  color: #06121a;
}
.brand small { color: var(--text-muted); font-weight: 500; }

.chip-nav {
  display: flex;
  gap: 6px;
  overflow-x: auto;
  scrollbar-width: none;
  flex: 1;
}
.chip-nav::-webkit-scrollbar { display: none; }
.chip {
  flex-shrink: 0;
  padding: 6px 14px;
  border-radius: 999px;
  border: 1px solid var(--border);
  color: var(--text-dim);
  font-size: 13.5px;
  text-decoration: none;
  transition: all 0.2s;
}
.chip:hover { border-color: var(--teal); color: var(--teal); }
.chip.on {
  background: linear-gradient(135deg, rgba(0, 212, 170, 0.16), rgba(56, 163, 255, 0.16));
  border-color: var(--teal);
  color: var(--teal);
}

.read-progress {
  position: fixed;
  top: 60px; left: 0;
  height: 3px;
  width: 0%;
  background: var(--grad);
  z-index: 101;
  transition: width 0.1s linear;
}

/* ---------- 布局 ---------- */
.container { max-width: 1080px; margin: 0 auto; padding: 0 24px; }
main { padding-top: 84px; }

/* ---------- 首页 Hero ---------- */
.hero {
  text-align: center;
  padding: 64px 0 40px;
}
.hero .kicker {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 18px;
  border-radius: 999px;
  border: 1px solid rgba(0, 212, 170, 0.4);
  color: var(--teal);
  font-size: 14px;
  background: rgba(0, 212, 170, 0.07);
  margin-bottom: 22px;
}
.hero h1 {
  font-size: clamp(34px, 5.4vw, 56px);
  line-height: 1.25;
  font-weight: 900;
  letter-spacing: 1px;
}
.hero h1 .grad-text {
  background: var(--grad);
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}
.hero .sub {
  max-width: 720px;
  margin: 20px auto 0;
  color: var(--text-dim);
  font-size: 17px;
}
.hero .cta-row {
  margin-top: 30px;
  display: flex;
  gap: 14px;
  justify-content: center;
  flex-wrap: wrap;
}
.btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 12px 26px;
  border-radius: 12px;
  font-weight: 700;
  font-size: 15px;
  text-decoration: none;
  transition: transform 0.15s, box-shadow 0.15s;
}
.btn:hover { transform: translateY(-2px); }
.btn-primary { background: var(--grad); color: #06121a; box-shadow: 0 6px 24px rgba(0, 212, 170, 0.35); }
.btn-ghost { border: 1px solid var(--border-2); color: var(--text); background: var(--card); }
.btn-ghost:hover { border-color: var(--blue); color: var(--blue); }

/* ---------- 章节卡片 ---------- */
.section-title {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 56px 0 8px;
}
.section-title .bar {
  width: 6px; height: 26px;
  border-radius: 4px;
  background: var(--grad);
}
.section-title h2 { font-size: 26px; font-weight: 800; }
.section-sub { color: var(--text-muted); margin-bottom: 26px; font-size: 15px; }

.chapter-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(320px, 1fr));
  gap: 20px;
}
.chapter-card {
  position: relative;
  display: block;
  padding: 24px;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  background: linear-gradient(160deg, var(--card) 0%, var(--bg-soft) 100%);
  text-decoration: none;
  color: var(--text);
  overflow: hidden;
  transition: transform 0.2s, border-color 0.2s, box-shadow 0.2s;
}
.chapter-card:hover {
  transform: translateY(-4px);
  border-color: var(--teal);
  box-shadow: var(--shadow);
}
.chapter-card .no {
  position: absolute;
  top: 14px; right: 20px;
  font-size: 44px;
  font-weight: 900;
  color: transparent;
  -webkit-text-stroke: 1.5px var(--border-2);
  line-height: 1;
}
.chapter-card .tag {
  display: inline-block;
  font-size: 12.5px;
  font-weight: 700;
  padding: 3px 12px;
  border-radius: 999px;
  margin-bottom: 12px;
}
.tag-t1 { background: rgba(56, 163, 255, 0.15); color: var(--blue); }
.tag-t2 { background: rgba(0, 212, 170, 0.15); color: var(--teal); }
.tag-t3 { background: rgba(139, 92, 246, 0.15); color: var(--purple); }
.tag-t4 { background: rgba(245, 166, 35, 0.15); color: var(--orange); }
.tag-t5 { background: rgba(236, 72, 153, 0.15); color: var(--pink); }
.tag-t6 { background: rgba(74, 222, 128, 0.15); color: var(--green); }
.tag-t7 { background: rgba(250, 204, 21, 0.15); color: var(--yellow); }
.tag-t8 { background: rgba(255, 255, 255, 0.12); color: var(--text); }

.chapter-card h3 { font-size: 19px; margin-bottom: 8px; }
.chapter-card p { color: var(--text-dim); font-size: 14.5px; }
.chapter-card .learn {
  margin-top: 14px;
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}
.chapter-card .learn span {
  font-size: 12px;
  padding: 2px 10px;
  border-radius: 6px;
  background: var(--card-3);
  color: var(--text-dim);
  border: 1px solid var(--border);
}

/* ---------- 章节页 Hero ---------- */
.ch-hero {
  padding: 44px 0 26px;
  border-bottom: 1px solid var(--border);
  margin-bottom: 30px;
}
.ch-hero .crumb { color: var(--text-muted); font-size: 13.5px; margin-bottom: 12px; }
.ch-hero .crumb a { color: var(--text-muted); text-decoration: none; }
.ch-hero .crumb a:hover { color: var(--teal); }
.ch-hero h1 { font-size: clamp(28px, 4.5vw, 42px); font-weight: 900; }
.ch-hero .meta { display: flex; gap: 10px; flex-wrap: wrap; margin-top: 14px; }
.ch-hero .meta .pill {
  font-size: 13px;
  padding: 4px 14px;
  border-radius: 999px;
  border: 1px solid var(--border);
  color: var(--text-dim);
}
.ch-hero .lead {
  margin-top: 16px;
  color: var(--text-dim);
  font-size: 16.5px;
  max-width: 860px;
}

/* ---------- 小节 ---------- */
.section {
  margin: 44px 0;
}
.section > h2 {
  display: flex;
  align-items: center;
  gap: 10px;
  font-size: 24px;
  font-weight: 800;
  margin-bottom: 6px;
}
.section > h2 .sec-no {
  font-size: 14px;
  font-weight: 800;
  color: #06121a;
  background: var(--grad);
  border-radius: 8px;
  padding: 3px 10px;
}
.section > h2 .sec-no.alt { background: var(--grad-2); }
.section > h2 .sec-no.alt3 { background: var(--grad-3); }
.section > .sec-desc { color: var(--text-muted); margin-bottom: 18px; font-size: 15px; }

/* 要点列表 */
.points { margin: 18px 0 24px; display: grid; gap: 10px; }
.points li {
  list-style: none;
  position: relative;
  padding-left: 26px;
  color: var(--text-dim);
  font-size: 15.5px;
}
.points li::before {
  content: "▸";
  position: absolute;
  left: 4px;
  color: var(--teal);
  font-weight: 900;
}
.points li strong { color: var(--text); }

/* ---------- 图容器 ---------- */
.fig {
  margin: 22px 0;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  background: linear-gradient(180deg, var(--card) 0%, var(--bg-soft) 100%);
  padding: 20px;
  box-shadow: var(--shadow-sm);
}
.fig svg { display: block; width: 100%; height: auto; }
.fig .cap {
  margin-top: 14px;
  padding-top: 12px;
  border-top: 1px dashed var(--border);
  color: var(--text-muted);
  font-size: 13.5px;
  line-height: 1.7;
}
.fig .cap b { color: var(--teal); font-weight: 700; }

/* ---------- 心法卡片 ---------- */
.mind {
  display: flex;
  gap: 16px;
  align-items: flex-start;
  border-radius: var(--radius-lg);
  border: 1px solid rgba(0, 212, 170, 0.35);
  background: linear-gradient(135deg, rgba(0, 212, 170, 0.09), rgba(56, 163, 255, 0.06));
  padding: 20px 24px;
  margin: 26px 0;
}
.mind .icon {
  flex-shrink: 0;
  width: 42px; height: 42px;
  border-radius: 12px;
  background: var(--grad);
  display: grid; place-items: center;
  font-size: 20px;
  color: #06121a;
}
.mind h4 { font-size: 16px; margin-bottom: 4px; color: var(--teal); }
.mind p { color: var(--text-dim); font-size: 15px; }

/* ---------- 视频 ---------- */
.video-wrap {
  margin: 22px 0;
  border-radius: var(--radius-lg);
  overflow: hidden;
  border: 1px solid var(--border);
  background: #000;
  box-shadow: var(--shadow-sm);
}
.video-wrap .ratio {
  position: relative;
  width: 100%;
  padding-top: 56.25%;
}
.video-wrap iframe {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  border: 0;
}
.video-cap {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  padding: 12px 18px;
  background: var(--card);
  border-top: 1px solid var(--border);
  flex-wrap: wrap;
}
.video-cap .v-title { color: var(--text); font-size: 14.5px; font-weight: 600; }
.video-cap .v-link { color: var(--blue); font-size: 13px; text-decoration: none; }
.video-cap .v-link:hover { text-decoration: underline; }

/* ---------- 表格 ---------- */
.tbl-wrap { margin: 20px 0; overflow-x: auto; border-radius: var(--radius); border: 1px solid var(--border); }
table.data { width: 100%; border-collapse: collapse; font-size: 14.5px; min-width: 560px; }
table.data th {
  background: var(--card-3);
  color: var(--text);
  text-align: left;
  padding: 12px 16px;
  font-weight: 700;
  white-space: nowrap;
}
table.data td { padding: 11px 16px; border-top: 1px solid var(--border); color: var(--text-dim); }
table.data tr:nth-child(even) td { background: rgba(255, 255, 255, 0.02); }
table.data td b { color: var(--text); }

/* ---------- 步骤条 ---------- */
.steps { display: grid; gap: 12px; margin: 20px 0; counter-reset: step; }
.step {
  display: flex;
  gap: 16px;
  align-items: flex-start;
  padding: 16px 20px;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  background: var(--card);
  counter-increment: step;
}
.step .n {
  flex-shrink: 0;
  width: 34px; height: 34px;
  border-radius: 10px;
  background: var(--card-3);
  border: 1px solid var(--border-2);
  display: grid; place-items: center;
  font-weight: 800;
  color: var(--teal);
}
.step b { display: block; color: var(--text); margin-bottom: 2px; }
.step span { color: var(--text-dim); font-size: 14.5px; }

/* ---------- 上一章/下一章 ---------- */
.pager {
  display: flex;
  justify-content: space-between;
  gap: 16px;
  margin: 56px 0 20px;
}
.pager a {
  flex: 1;
  display: block;
  padding: 18px 22px;
  border-radius: var(--radius-lg);
  border: 1px solid var(--border);
  background: var(--card);
  text-decoration: none;
  color: var(--text);
  transition: border-color 0.2s, transform 0.2s;
  max-width: 340px;
}
.pager a:hover { border-color: var(--teal); transform: translateY(-2px); }
.pager a .dir { font-size: 12.5px; color: var(--text-muted); }
.pager a .t { font-size: 16px; font-weight: 700; margin-top: 2px; }
.pager a.next { text-align: right; margin-left: auto; }

/* ---------- 页脚 ---------- */
footer.site {
  margin-top: 60px;
  border-top: 1px solid var(--border);
  padding: 34px 0 60px;
  color: var(--text-muted);
  font-size: 13.5px;
  text-align: center;
}
footer.site .heart { color: var(--pink); }

/* ---------- 返回顶部 ---------- */
#toTop {
  position: fixed;
  right: 26px; bottom: 30px;
  width: 46px; height: 46px;
  border-radius: 14px;
  border: 1px solid var(--border-2);
  background: var(--card);
  color: var(--teal);
  font-size: 20px;
  cursor: pointer;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.25s, transform 0.25s;
  z-index: 99;
}
#toTop.show { opacity: 1; pointer-events: auto; }
#toTop:hover { transform: translateY(-3px); }

/* ---------- 响应式 ---------- */
@media (max-width: 860px) {
  .topbar { padding: 0 14px; gap: 10px; }
  .brand small { display: none; }
  .chip { font-size: 12.5px; padding: 5px 11px; }
  .chapter-grid { grid-template-columns: 1fr; }
  main { padding-top: 76px; }
  .pager { flex-direction: column; }
  .pager a { max-width: none; }
}