/* ============================================================
   深度学习入门站 · 设计系统
   通俗易懂 · 现代 · 中文排版
   ============================================================ */
:root {
  --bg: #f7f8fc;
  --bg-soft: #eef0f8;
  --surface: #ffffff;
  --surface-2: #f3f4fb;
  --text: #1e2433;
  --text-2: #5a6276;
  --text-3: #8b93a7;
  --line: #e3e6f0;
  --primary: #4f46e5;
  --primary-strong: #3730a3;
  --primary-soft: #eef0ff;
  --accent: #f59e0b;
  --accent-soft: #fef3d8;
  --success: #16a34a;
  --success-soft: #e8f8ee;
  --danger: #dc2626;
  --radius: 14px;
  --radius-sm: 9px;
  --shadow: 0 1px 3px rgba(30, 36, 51, .06), 0 8px 24px rgba(30, 36, 51, .06);
  --shadow-lg: 0 4px 12px rgba(30, 36, 51, .08), 0 16px 40px rgba(30, 36, 51, .10);
  --font-sans: "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans SC", "Source Han Sans SC", system-ui, -apple-system, sans-serif;
  --font-mono: "JetBrains Mono", "Cascadia Code", Consolas, "Courier New", monospace;
  --content-w: 760px;
}

[data-theme="dark"] {
  --bg: #0f1117;
  --bg-soft: #171a24;
  --surface: #1a1e2b;
  --surface-2: #222738;
  --text: #e7eaf3;
  --text-2: #a7aec4;
  --text-3: #6d7591;
  --line: #2b3145;
  --primary: #818cf8;
  --primary-strong: #a5b4fc;
  --primary-soft: #262b47;
  --accent: #fbbf24;
  --accent-soft: #3a3015;
  --success: #4ade80;
  --success-soft: #14301f;
  --danger: #f87171;
  --shadow: 0 1px 3px rgba(0, 0, 0, .4), 0 8px 24px rgba(0, 0, 0, .35);
  --shadow-lg: 0 4px 12px rgba(0, 0, 0, .5), 0 16px 40px rgba(0, 0, 0, .45);
}

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

html { scroll-behavior: smooth; }

body {
  font-family: var(--font-sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.8;
  font-size: 16.5px;
  -webkit-font-smoothing: antialiased;
  transition: background .25s, color .25s;
}

a { color: var(--primary); text-decoration: none; }
a:hover { color: var(--primary-strong); }

img { max-width: 100%; }

::selection { background: var(--primary); color: #fff; }

/* ---------- 顶部导航栏 ---------- */
.topbar {
  position: sticky; top: 0; z-index: 60;
  height: 60px;
  background: color-mix(in srgb, var(--surface) 86%, transparent);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--line);
  display: flex; align-items: center; gap: 14px;
  padding: 0 22px;
}
.topbar .brand {
  display: flex; align-items: center; gap: 10px;
  font-weight: 700; font-size: 17px; color: var(--text);
}
.topbar .brand .logo {
  width: 30px; height: 30px; border-radius: 8px;
  background: linear-gradient(135deg, var(--primary), #8b5cf6);
  display: grid; place-items: center; color: #fff; font-size: 15px;
}
.topbar .spacer { flex: 1; }
.topbar .theme-btn {
  border: 1px solid var(--line); background: var(--surface);
  color: var(--text-2); border-radius: 999px; padding: 6px 14px;
  font-size: 13.5px; cursor: pointer; transition: all .2s;
  font-family: var(--font-sans);
}
.topbar .theme-btn:hover { border-color: var(--primary); color: var(--primary); }
.topbar .menu-btn {
  display: none; border: 1px solid var(--line); background: var(--surface);
  color: var(--text); border-radius: 9px; width: 38px; height: 38px;
  cursor: pointer; font-size: 17px;
}

/* ---------- 布局 ---------- */
.layout { display: flex; align-items: flex-start; max-width: 1240px; margin: 0 auto; padding: 26px 22px 80px; gap: 34px; }

/* 侧边栏 */
.sidebar {
  position: sticky; top: 86px;
  width: 268px; flex-shrink: 0;
  max-height: calc(100vh - 110px);
  overflow-y: auto;
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 14px;
  box-shadow: var(--shadow);
}
.sidebar::-webkit-scrollbar { width: 6px; }
.sidebar::-webkit-scrollbar-thumb { background: var(--line); border-radius: 3px; }
.sidebar .side-title {
  font-size: 12px; font-weight: 700; letter-spacing: .12em;
  color: var(--text-3); text-transform: uppercase; padding: 6px 10px 8px;
}
.sidebar nav a {
  display: flex; gap: 10px; align-items: baseline;
  padding: 8px 10px; border-radius: 9px;
  color: var(--text-2); font-size: 14px; line-height: 1.5;
  transition: background .15s, color .15s;
}
.sidebar nav a:hover { background: var(--surface-2); color: var(--text); }
.sidebar nav a.active { background: var(--primary-soft); color: var(--primary); font-weight: 600; }
.sidebar nav a .num {
  font-family: var(--font-mono); font-size: 11.5px; color: var(--text-3);
  flex-shrink: 0; margin-top: 3px; min-width: 22px;
}
.sidebar nav a.active .num { color: var(--primary); }

/* 主内容 */
.main { flex: 1; min-width: 0; }

/* ---------- 章节卡片（首页） ---------- */
.hero {
  background: linear-gradient(135deg, var(--primary) 0%, #7c3aed 55%, #db2777 130%);
  border-radius: 20px; color: #fff;
  padding: 46px 44px; margin-bottom: 30px;
  box-shadow: var(--shadow-lg); position: relative; overflow: hidden;
}
.hero::after {
  content: ""; position: absolute; right: -80px; top: -80px;
  width: 300px; height: 300px; border-radius: 50%;
  background: radial-gradient(circle, rgba(255,255,255,.18), transparent 65%);
}
.hero .tag {
  display: inline-block; background: rgba(255,255,255,.18);
  border: 1px solid rgba(255,255,255,.3);
  padding: 3px 12px; border-radius: 999px; font-size: 12.5px;
  letter-spacing: .08em; margin-bottom: 14px;
}
.hero h1 { font-size: 34px; line-height: 1.35; margin-bottom: 12px; font-weight: 800; }
.hero p { font-size: 16px; line-height: 1.9; opacity: .94; max-width: 640px; }
.hero .cta { margin-top: 22px; display: flex; gap: 12px; flex-wrap: wrap; }
.hero .cta a {
  background: #fff; color: var(--primary-strong); font-weight: 700;
  padding: 10px 22px; border-radius: 999px; font-size: 15px;
  transition: transform .15s, box-shadow .15s;
}
.hero .cta a:hover { transform: translateY(-2px); box-shadow: 0 8px 20px rgba(0,0,0,.25); }
.hero .cta a.ghost { background: transparent; color: #fff; border: 1.5px solid rgba(255,255,255,.5); }

.section-title {
  font-size: 20px; font-weight: 800; margin: 34px 0 16px;
  display: flex; align-items: center; gap: 10px;
}
.section-title::before {
  content: ""; width: 6px; height: 22px; border-radius: 3px;
  background: linear-gradient(180deg, var(--primary), #8b5cf6);
}

.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(300px, 1fr)); gap: 16px; }
.card {
  background: var(--surface); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 20px;
  transition: transform .18s, box-shadow .18s, border-color .18s;
  display: block; color: var(--text);
}
.card:hover { transform: translateY(-3px); box-shadow: var(--shadow-lg); border-color: var(--primary); }
.card .c-head { display: flex; align-items: center; gap: 12px; margin-bottom: 10px; }
.card .c-ico {
  width: 40px; height: 40px; border-radius: 11px; flex-shrink: 0;
  display: grid; place-items: center; font-size: 19px;
  background: var(--primary-soft); color: var(--primary);
}
.card h3 { font-size: 16.5px; font-weight: 700; line-height: 1.4; }
.card p { font-size: 13.8px; color: var(--text-2); line-height: 1.75; }
.card .c-tag {
  display: inline-block; margin-top: 12px; font-size: 12px;
  color: var(--text-3); font-family: var(--font-mono);
}

/* ---------- 章节正文 ---------- */
.article {
  background: var(--surface); border: 1px solid var(--line);
  border-radius: 20px; padding: 46px 52px;
  box-shadow: var(--shadow);
  max-width: var(--content-w); margin: 0 auto;
}
@media (max-width: 860px) { .article { padding: 30px 22px; } }

.article .crumb {
  font-size: 13px; color: var(--text-3); margin-bottom: 14px;
  display: flex; flex-wrap: wrap; gap: 6px; align-items: center;
}
.article .crumb a { color: var(--text-3); }
.article .crumb a:hover { color: var(--primary); }

.article h1 {
  font-size: 30px; font-weight: 800; line-height: 1.4;
  margin-bottom: 8px; letter-spacing: -.01em;
}
.article .subtitle { font-size: 15.5px; color: var(--text-2); margin-bottom: 18px; }

.article .lead {
  background: var(--primary-soft); border-left: 4px solid var(--primary);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  padding: 16px 20px; margin: 20px 0 30px;
  font-size: 15.5px; line-height: 1.85; color: var(--text);
}

.article h2 {
  font-size: 22px; font-weight: 800; margin: 42px 0 14px;
  padding-bottom: 8px; border-bottom: 2px solid var(--line);
  scroll-margin-top: 90px;
}
.article h3 { font-size: 17.5px; font-weight: 700; margin: 30px 0 10px; scroll-margin-top: 90px; }
.article h4 { font-size: 16px; font-weight: 700; margin: 24px 0 8px; }
.article p { margin: 12px 0; }
.article ul, .article ol { margin: 12px 0 12px 24px; }
.article li { margin: 6px 0; }
.article strong { color: var(--text); font-weight: 700; }

.article blockquote {
  border-left: 4px solid var(--accent); background: var(--accent-soft);
  padding: 14px 18px; border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  margin: 18px 0; color: var(--text);
}
.article blockquote p { margin: 6px 0; }

/* 类比框 */
.analogy {
  display: flex; gap: 14px;
  background: linear-gradient(135deg, var(--primary-soft), var(--surface-2));
  border: 1px solid color-mix(in srgb, var(--primary) 30%, var(--line));
  border-radius: var(--radius); padding: 18px 20px; margin: 20px 0;
}
.analogy .a-ico { font-size: 26px; flex-shrink: 0; line-height: 1.4; }
.analogy .a-body { font-size: 15px; line-height: 1.8; }
.analogy .a-body .a-label {
  display: inline-block; font-size: 12px; font-weight: 700; letter-spacing: .1em;
  color: var(--primary); margin-bottom: 4px;
}

/* 要点框 / 提示框 */
.callout {
  border-radius: var(--radius); padding: 16px 20px; margin: 18px 0;
  display: flex; gap: 12px; font-size: 15px; line-height: 1.8;
}
.callout .c-ico { font-size: 20px; flex-shrink: 0; }
.callout.key { background: var(--success-soft); border: 1px solid color-mix(in srgb, var(--success) 35%, var(--line)); }
.callout.warn { background: var(--accent-soft); border: 1px solid color-mix(in srgb, var(--accent) 40%, var(--line)); }
.callout.tip { background: var(--primary-soft); border: 1px solid color-mix(in srgb, var(--primary) 30%, var(--line)); }

/* 代码块 */
.article pre {
  background: #0f172a; color: #e2e8f0;
  border-radius: var(--radius-sm); padding: 18px 20px;
  overflow-x: auto; margin: 18px 0;
  font-family: var(--font-mono); font-size: 13.5px; line-height: 1.7;
  box-shadow: var(--shadow);
}
.article code {
  font-family: var(--font-mono); font-size: .88em;
  background: var(--surface-2); color: var(--primary-strong);
  padding: 2px 6px; border-radius: 5px;
}
.article pre code { background: none; color: inherit; padding: 0; font-size: inherit; }
[data-theme="dark"] .article pre { background: #0b0e16; }
[data-theme="dark"] .article code:not(pre code) { color: #a5b4fc; }

/* 表格 */
.article table {
  width: 100%; border-collapse: collapse; margin: 20px 0;
  font-size: 14.5px;
}
.article th, .article td {
  border: 1px solid var(--line); padding: 10px 14px; text-align: left;
}
.article th { background: var(--surface-2); font-weight: 700; }
.article tr:nth-child(even) td { background: var(--surface-2); }

/* KaTeX 居中 */
.katex-display { margin: 18px 0 !important; overflow-x: auto; overflow-y: hidden; padding: 4px 0; }

/* 练习区 */
.quiz {
  background: var(--surface-2); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 20px 22px; margin: 22px 0;
}
.quiz h4 { margin-bottom: 10px; display: flex; align-items: center; gap: 8px; }
.quiz .q { margin: 12px 0; font-size: 15px; }
.quiz .options { display: grid; gap: 8px; margin-top: 8px; }
.quiz .opt {
  display: flex; gap: 10px; align-items: flex-start;
  border: 1px solid var(--line); border-radius: 9px;
  padding: 10px 14px; cursor: pointer; background: var(--surface);
  transition: border-color .15s, background .15s; font-size: 14.5px;
}
.quiz .opt:hover { border-color: var(--primary); }
.quiz .opt input { margin-top: 5px; accent-color: var(--primary); }
.quiz .opt.correct { border-color: var(--success); background: var(--success-soft); }
.quiz .opt.wrong { border-color: var(--danger); background: color-mix(in srgb, var(--danger) 8%, var(--surface)); }
.quiz .answer-note { display: none; margin-top: 10px; font-size: 14px; color: var(--text-2); border-top: 1px dashed var(--line); padding-top: 10px; }
.quiz .answer-note.show { display: block; }
.quiz .check-btn {
  margin-top: 14px; background: var(--primary); color: #fff; border: none;
  border-radius: 9px; padding: 9px 20px; font-size: 14px; cursor: pointer;
  font-family: var(--font-sans); transition: opacity .15s;
}
.quiz .check-btn:hover { opacity: .88; }

/* 上下章导航 */
.pager {
  display: flex; justify-content: space-between; gap: 14px;
  margin-top: 40px; padding-top: 24px; border-top: 1px solid var(--line);
}
.pager a {
  flex: 1; max-width: 46%;
  background: var(--surface-2); border: 1px solid var(--line);
  border-radius: var(--radius); padding: 14px 18px;
  color: var(--text-2); transition: all .18s; display: block;
}
.pager a:hover { border-color: var(--primary); color: var(--primary); transform: translateY(-2px); box-shadow: var(--shadow); }
.pager a .dir { font-size: 12px; color: var(--text-3); display: block; margin-bottom: 2px; }
.pager a .t { font-weight: 700; font-size: 14.5px; color: var(--text); }
.pager a.next { text-align: right; margin-left: auto; }

/* 页脚 */
.footer {
  text-align: center; color: var(--text-3); font-size: 13px;
  padding: 30px 20px 46px;
}

/* 阅读进度条 */
.progress {
  position: fixed; top: 0; left: 0; height: 3px; width: 0;
  background: linear-gradient(90deg, var(--primary), #8b5cf6, var(--accent));
  z-index: 100; transition: width .08s linear;
}

/* 移动端 */
@media (max-width: 960px) {
  .sidebar {
    position: fixed; left: 0; top: 60px; bottom: 0; z-index: 55;
    transform: translateX(-105%); transition: transform .25s ease;
    max-height: none; border-radius: 0; border-left: none; border-top: none;
    width: 300px;
  }
  .sidebar.open { transform: translateX(0); }
  .topbar .menu-btn { display: grid; place-items: center; }
  .layout { padding: 16px 14px 60px; gap: 0; }
  .hero { padding: 30px 24px; }
  .hero h1 { font-size: 25px; }
  .article { padding: 26px 18px; border-radius: 14px; }
  .article h1 { font-size: 24px; }
  .grid { grid-template-columns: 1fr; }
}
@media (max-width: 480px) {
  .pager { flex-direction: column; }
  .pager a { max-width: 100%; }
}


/* 图解样式（dl-diagrams） */
.article figure.dl-fig{margin:1.6em auto;text-align:center;max-width:860px}
.article figure.dl-fig img{width:100%;height:auto;border-radius:14px;background:#fff;box-shadow:0 8px 24px -8px rgba(15,23,42,.18);border:1px solid rgba(148,163,184,.25)}
.article figure.dl-fig figcaption{margin-top:.7em;font-size:13.5px;color:#64748b}