:root {
  --color-bg: #faf9f6;
  --color-bg-pure: #ffffff;
  --color-bg-section: #f5f3ee;
  --color-bg-tint: #f0ede5;
  --color-text: #18181b;
  --color-text-soft: #3f3f46;
  --color-text-muted: #71717a;
  --color-accent: #1e40af;
  --color-accent-hover: #1e3a8a;
  --color-accent-light: #3b82f6;
  --color-accent-soft: rgba(30, 64, 175, 0.08);
  --color-accent-glow: rgba(30, 64, 175, 0.28);
  --color-gold: #b45309;
  --color-border: #e7e5e4;
  --color-border-strong: #d4d4d8;
  --color-divider: rgba(63, 63, 70, 0.08);

  --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.04);
  --shadow-md: 0 4px 14px -2px rgba(0, 0, 0, 0.06), 0 2px 6px -2px rgba(0, 0, 0, 0.04);
  --shadow-lg: 0 12px 28px -8px rgba(0, 0, 0, 0.10), 0 4px 10px -4px rgba(0, 0, 0, 0.05);
  --shadow-book:
    0 1px 1px rgba(0, 0, 0, 0.08),
    0 5px 10px rgba(0, 0, 0, 0.10),
    0 22px 36px -10px rgba(0, 0, 0, 0.22);
  --ring-focus: 0 0 0 3px rgba(30, 64, 175, 0.22);

  --max-width: 1080px;
  --radius-sm: 6px;
  --radius-md: 12px;
  --radius-lg: 20px;

  --ease-out: cubic-bezier(0.22, 0.61, 0.36, 1);
  --ease-spring: cubic-bezier(0.34, 1.2, 0.64, 1);

  --font-serif: "Noto Serif SC", "Source Han Serif SC", "Songti SC", Georgia, "Times New Roman", serif;
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Arial, sans-serif;
  --font-mono: ui-monospace, "SF Mono", "JetBrains Mono", Menlo, Consolas, monospace;
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

* { box-sizing: border-box; }

html {
  font-size: 17px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  color: var(--color-text);
  line-height: 1.7;
  background-color: var(--color-bg);
  background-image:
    radial-gradient(at 0% 0%, rgba(30, 64, 175, 0.05) 0px, transparent 50%),
    radial-gradient(at 100% 100%, rgba(180, 83, 9, 0.04) 0px, transparent 50%);
  background-attachment: fixed;
  font-feature-settings: "kern", "liga";
}

.wrapper {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 32px;
}

/* ---------- Header ---------- */
.site-header {
  border-bottom: 1px solid var(--color-border);
  background: rgba(250, 249, 246, 0.78);
  backdrop-filter: saturate(180%) blur(14px);
  -webkit-backdrop-filter: saturate(180%) blur(14px);
  position: sticky;
  top: 0;
  z-index: 50;
}

.site-header .wrapper {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 72px;
  flex-wrap: wrap;
}

.site-title {
  font-family: var(--font-serif);
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--color-text);
  text-decoration: none;
  letter-spacing: 0.01em;
}

.site-nav {
  display: flex;
  gap: 32px;
}

.site-nav a {
  color: var(--color-text-soft);
  text-decoration: none;
  font-size: 0.92rem;
  font-weight: 500;
  position: relative;
  padding: 6px 0;
  transition: color 0.2s var(--ease-out);
}

.site-nav a::after {
  content: '';
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 1.5px;
  background: linear-gradient(90deg, var(--color-accent), var(--color-accent-light));
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.25s var(--ease-out);
  border-radius: 1px;
}

.site-nav a:hover { color: var(--color-text); }
.site-nav a:hover::after { transform: scaleX(1); }

.site-nav a.is-active {
  color: var(--color-text);
}

.site-nav a.is-active::after {
  transform: scaleX(1);
  transform-origin: left;
}

.site-title {
  transition: color 0.2s var(--ease-out);
}

.site-title:hover { color: var(--color-accent); }

/* GitHub link with star badge */
.nav-gh {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  color: var(--color-text-soft);
}

.nav-gh:hover { color: var(--color-text); }

.nav-gh-icon {
  display: block;
  flex-shrink: 0;
}

.gh-stars {
  display: inline-flex;
  align-items: center;
  gap: 3px;
  padding: 2px 8px 2px 6px;
  border-radius: 999px;
  background: var(--color-bg-section);
  border: 1px solid var(--color-border);
  font-size: 0.74rem;
  font-weight: 600;
  color: var(--color-text-soft);
  font-feature-settings: "tnum";
  line-height: 1.2;
  transition: all 0.25s ease;
  min-width: 28px;
  justify-content: center;
}

.gh-stars svg {
  color: #d4d4d8;
  transition: color 0.25s ease;
}

.gh-stars.loaded {
  background: linear-gradient(135deg, rgba(254, 243, 199, 0.85), rgba(253, 230, 138, 0.85));
  border-color: rgba(251, 191, 36, 0.45);
  color: #78350f;
}

.gh-stars.loaded svg { color: #f59e0b; }

.gh-stars.failed { display: none; }

.book-card-mini__foot .gh-stars {
  padding: 3px 9px 3px 7px;
  font-size: 0.78rem;
  line-height: 1.4;
  gap: 4px;
  min-width: 36px;
}

/* ---------- Content ---------- */
.site-content {
  padding: 64px 0 100px;
}

h1, h2, h3, h4 {
  font-family: var(--font-serif);
  font-weight: 700;
  line-height: 1.25;
  margin-top: 2.5rem;
  margin-bottom: 1rem;
  color: var(--color-text);
  letter-spacing: -0.015em;
}

h1 {
  font-size: 3rem;
  margin-top: 0;
  letter-spacing: -0.025em;
  line-height: 1.1;
  font-weight: 900;
}

h2 {
  font-size: 1.65rem;
  padding-bottom: 0.55rem;
  margin-top: 3.2rem;
  position: relative;
  border-bottom: 1px solid var(--color-border);
}

h2::after {
  content: '';
  position: absolute;
  left: 0;
  bottom: -1px;
  width: 44px;
  height: 2px;
  background: var(--color-accent);
  border-radius: 2px;
}

h3 {
  font-size: 1.22rem;
  margin-top: 2rem;
  color: var(--color-text-soft);
}

p { margin: 0.9rem 0; }

a {
  color: var(--color-accent);
  text-decoration: none;
  transition: color 0.15s var(--ease-out), border-color 0.15s var(--ease-out);
  border-bottom: 1px solid transparent;
}

a:hover {
  color: var(--color-accent-hover);
  border-bottom-color: currentColor;
}

:focus-visible {
  outline: none;
  box-shadow: var(--ring-focus);
  border-radius: 4px;
}

a:focus-visible {
  border-bottom-color: transparent;
}

img { max-width: 100%; height: auto; }

hr {
  border: 0;
  height: 1px;
  background: linear-gradient(90deg, transparent, var(--color-border-strong) 30%, var(--color-border-strong) 70%, transparent);
  margin: 48px 0;
  position: relative;
}

hr::after {
  content: '·';
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -55%);
  background: var(--color-bg);
  color: var(--color-text-muted);
  font-size: 1.2rem;
  line-height: 1;
  padding: 0 12px;
  letter-spacing: 0.4em;
}

blockquote {
  margin: 1.4rem 0;
  padding: 14px 22px;
  color: var(--color-text-soft);
  background: var(--color-bg-section);
  border-left: 3px solid var(--color-accent);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

blockquote > :first-child { margin-top: 0; }
blockquote > :last-child { margin-bottom: 0; }

ul, ol { padding-left: 1.6rem; }
li { margin: 6px 0; }
li::marker { color: var(--color-text-muted); }

code {
  font-family: var(--font-mono);
  background: var(--color-bg-section);
  border: 1px solid var(--color-border);
  border-radius: 4px;
  padding: 1px 6px;
  font-size: 0.86em;
  color: var(--color-text);
}

pre {
  background: #0f1115;
  color: #e4e4e7;
  border: 1px solid #27272a;
  border-radius: var(--radius-md);
  padding: 20px 22px 20px 22px;
  overflow-x: auto;
  font-size: 0.85em;
  line-height: 1.65;
  box-shadow: var(--shadow-md);
  position: relative;
}

pre::before {
  content: '';
  position: absolute;
  top: 0;
  left: 20px;
  right: 20px;
  height: 2px;
  background: linear-gradient(90deg, var(--color-accent-light), transparent 70%);
  border-radius: 0 0 2px 2px;
  opacity: 0.65;
}

pre code {
  background: none;
  border: none;
  padding: 0;
  color: inherit;
  font-size: inherit;
  display: block;
  margin-top: 0;
}

/* Scrollbar inside code blocks (Webkit) */
pre::-webkit-scrollbar { height: 8px; }
pre::-webkit-scrollbar-thumb { background: #3f3f46; border-radius: 999px; }
pre::-webkit-scrollbar-track { background: transparent; }

/* ---------- Syntax highlighting (Rouge tokens, dark theme) ---------- */
.highlight .c, .highlight .c1, .highlight .cm, .highlight .cs, .highlight .cp { color: #71717a; font-style: italic; }       /* comments */
.highlight .k, .highlight .kd, .highlight .kn, .highlight .kp, .highlight .kr, .highlight .kt { color: #c4b5fd; }            /* keywords */
.highlight .s, .highlight .s1, .highlight .s2, .highlight .sb, .highlight .sc, .highlight .sx, .highlight .se { color: #86efac; } /* strings */
.highlight .mi, .highlight .mf, .highlight .mh, .highlight .mo, .highlight .il { color: #fdba74; }                           /* numbers */
.highlight .nb, .highlight .nf, .highlight .nx { color: #93c5fd; }                                                            /* builtins / functions */
.highlight .nc, .highlight .nn, .highlight .ne { color: #fcd34d; }                                                            /* class / namespace */
.highlight .na, .highlight .nl, .highlight .nt { color: #f9a8d4; }                                                            /* attributes / labels / tags */
.highlight .o, .highlight .p { color: #a1a1aa; }                                                                              /* operators / punctuation */
.highlight .err { color: #fca5a5; }                                                                                           /* errors */
.highlight .gi { color: #86efac; }                                                                                            /* diff insert */
.highlight .gd { color: #fca5a5; }                                                                                            /* diff delete */

table {
  border-collapse: separate;
  border-spacing: 0;
  width: 100%;
  margin: 1.2rem 0;
  font-size: 0.94em;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  overflow: hidden;
}

th, td {
  border-bottom: 1px solid var(--color-border);
  padding: 10px 14px;
  text-align: left;
}

tbody tr:last-child td { border-bottom: 0; }

th + th, td + td { border-left: 1px solid var(--color-border); }

thead th {
  background: var(--color-bg-section);
  font-weight: 600;
  color: var(--color-text);
  font-size: 0.92em;
  letter-spacing: 0.01em;
}

tbody tr {
  transition: background 0.15s var(--ease-out);
}

tbody tr:hover { background: var(--color-bg-section); }

/* ---------- Eyebrow / labels ---------- */
.eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  font-family: var(--font-sans);
  font-size: 0.72rem;
  font-weight: 700;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--color-accent);
  margin: 0 0 0.9rem;
  padding: 4px 12px 4px 10px;
  background: var(--color-accent-soft);
  border: 1px solid rgba(30, 64, 175, 0.16);
  border-radius: 999px;
  line-height: 1.4;
}

.eyebrow::before {
  content: '';
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: currentColor;
  flex-shrink: 0;
}

/* ---------- Book card (Hero) ---------- */
.book-card {
  display: flex;
  gap: 48px;
  align-items: center;
  margin: 36px 0 56px;
  padding: 48px 44px;
  background: linear-gradient(135deg, #ffffff 0%, #faf8f3 100%);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  position: relative;
  overflow: hidden;
}

.book-card::before {
  content: '';
  position: absolute;
  top: -120px;
  right: -120px;
  width: 380px;
  height: 380px;
  background:
    radial-gradient(circle at 30% 30%, rgba(30, 64, 175, 0.12) 0%, transparent 60%),
    radial-gradient(circle at 70% 70%, rgba(59, 130, 246, 0.08) 0%, transparent 60%);
  pointer-events: none;
  filter: blur(8px);
}

.book-card::after {
  content: '';
  position: absolute;
  bottom: -100px;
  left: -100px;
  width: 300px;
  height: 300px;
  background: radial-gradient(circle, rgba(180, 83, 9, 0.08) 0%, transparent 60%);
  pointer-events: none;
  filter: blur(20px);
}

.book-card img {
  width: 220px;
  flex-shrink: 0;
  border-radius: var(--radius-sm);
  box-shadow: var(--shadow-book);
  transform: rotate(-2deg) perspective(800px) rotateY(-4deg);
  transition: transform 0.5s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
  z-index: 1;
}

.book-card:hover img {
  transform: rotate(0deg) perspective(800px) rotateY(0deg) scale(1.04);
}

.book-card .book-info {
  flex: 1;
  min-width: 0;
  position: relative;
  z-index: 1;
}

.book-card .book-info > :first-child { margin-top: 0; }
.book-card .book-info > :last-child { margin-bottom: 0; }

/* ---------- Buttons ---------- */
.btn-row {
  display: flex;
  gap: 12px;
  margin-top: 24px;
  flex-wrap: wrap;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 10px 20px;
  border-radius: var(--radius-sm);
  font-size: 0.92rem;
  font-weight: 500;
  text-decoration: none;
  transition: transform 0.2s var(--ease-out),
              box-shadow 0.2s var(--ease-out),
              background 0.2s var(--ease-out),
              border-color 0.2s var(--ease-out),
              color 0.2s var(--ease-out);
  border: 1px solid transparent;
  cursor: pointer;
  font-family: var(--font-sans);
  line-height: 1.4;
}

.btn:hover { border-bottom-color: transparent; }

.btn:focus-visible {
  outline: none;
  box-shadow: var(--ring-focus);
}

.btn-primary {
  background: linear-gradient(135deg, var(--color-accent) 0%, var(--color-accent-light) 100%);
  color: #fff;
  box-shadow: 0 4px 14px -3px var(--color-accent-glow);
}

.btn-primary:hover {
  color: #fff;
  transform: translateY(-1px);
  box-shadow: 0 10px 22px -6px var(--color-accent-glow);
}

.btn-secondary {
  background: var(--color-bg-pure);
  color: var(--color-text);
  border-color: var(--color-border-strong);
}

.btn-secondary:hover {
  background: var(--color-bg-pure);
  border-color: var(--color-accent);
  color: var(--color-accent);
  transform: translateY(-1px);
  box-shadow: var(--shadow-sm);
}

/* ---------- Home hero ---------- */
.home-hero {
  margin: 8px 0 44px;
  padding: 8px 0 0;
  position: relative;
}

.home-hero h1 {
  font-size: 2.5rem;
  margin: 4px 0 18px;
  letter-spacing: -0.022em;
  line-height: 1.15;
}

.home-hero h1 .accent {
  background: linear-gradient(135deg, var(--color-accent) 0%, var(--color-accent-light) 100%);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
  color: var(--color-accent);
}

.home-hero__lede {
  font-size: 1.05rem;
  color: var(--color-text-soft);
  line-height: 1.8;
  /* 仅在中文标点处换行，避免「大模型与/智能体」这类专有名词被劈开 */
  word-break: keep-all;
  overflow-wrap: break-word;
}

.home-hero__lede a {
  border-bottom: 1px dotted currentColor;
}

.home-hero__lede a:hover {
  border-bottom-style: solid;
}

/* Keep an inline phrase from breaking across lines (mainly Chinese terms) */
.nobreak { white-space: nowrap; }

/* ---------- Book grid (Home shelf) ---------- */
.book-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 22px;
  margin: 32px 0 56px;
}

.book-card-mini {
  display: flex;
  gap: 20px;
  padding: 22px;
  background: var(--color-bg-pure);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  text-decoration: none;
  color: inherit;
  transition: transform 0.25s var(--ease-out),
              box-shadow 0.25s var(--ease-out),
              border-color 0.25s var(--ease-out);
  position: relative;
  overflow: hidden;
}

.book-card-mini::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--color-accent), var(--color-accent-light));
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.35s var(--ease-out);
}

.book-card-mini:hover {
  border-color: var(--color-border-strong);
  text-decoration: none;
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

.book-card-mini:hover::before { transform: scaleX(1); }

.book-card-mini__cover img,
.book-card-mini__cover .cover-placeholder {
  transition: transform 0.35s var(--ease-out);
}

.book-card-mini:hover .book-card-mini__cover img,
.book-card-mini:hover .book-card-mini__cover .cover-placeholder {
  transform: translateY(-2px);
}

.book-card-mini:hover .book-card-mini__cta {
  color: var(--color-accent-hover);
}

.book-card-mini__cover {
  flex-shrink: 0;
  align-self: flex-start;
  width: 110px;
  position: relative;
  aspect-ratio: 600 / 848;
}

.book-card-mini__cover img {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  border-radius: var(--radius-sm);
  box-shadow: var(--shadow-book);
  display: block;
  object-fit: cover;
  z-index: 1;
}

/* Fallback rendered behind <img>; visible when image 404s and the img hides itself */
.cover-placeholder {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 10px;
  padding: 14px 12px;
  text-align: center;
  background: linear-gradient(160deg, #f5f3ee 0%, #e7e5e4 50%, #d6d3d0 100%);
  border-radius: var(--radius-sm);
  box-shadow: var(--shadow-book);
  color: var(--color-text-muted);
  overflow: hidden;
}

.cover-placeholder::before {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0;
  height: 4px;
  background: var(--color-accent);
}

.cover-placeholder__icon {
  color: var(--color-accent);
  opacity: 0.55;
  flex-shrink: 0;
}

.cover-placeholder__title {
  font-family: var(--font-serif);
  font-weight: 700;
  color: var(--color-text-soft);
  font-size: 0.78rem;
  line-height: 1.35;
}

.cover-placeholder--lg {
  gap: 16px;
  padding: 20px 16px;
}

.cover-placeholder--lg .cover-placeholder__title {
  font-size: 1.05rem;
}

.book-badge {
  position: absolute;
  top: 8px;
  right: -6px;
  background: var(--color-gold);
  color: #fff;
  font-size: 0.68rem;
  font-weight: 600;
  padding: 3px 8px;
  border-radius: 3px;
  letter-spacing: 0.04em;
  box-shadow: 0 2px 6px rgba(180, 83, 9, 0.3);
}

.book-badge--lg {
  font-size: 0.78rem;
  padding: 5px 12px;
  top: 14px;
  right: -10px;
}

.book-card-mini__body {
  flex: 1;
  min-width: 0;
  display: flex;
  flex-direction: column;
}

.book-card-mini__title {
  font-family: var(--font-serif);
  font-size: 1.15rem;
  font-weight: 700;
  margin: 0 0 4px;
  color: var(--color-text);
  line-height: 1.3;
}

.book-card-mini__subtitle {
  font-size: 0.82rem;
  color: var(--color-text-muted);
  margin: 0 0 10px;
}

.book-card-mini__blurb {
  font-size: 0.9rem;
  color: var(--color-text-soft);
  line-height: 1.6;
  margin: 0 0 12px;
  flex: 1;
}

.book-card-mini__foot {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  margin-top: auto;
  flex-wrap: wrap;
}

.book-card-mini__cta {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--color-accent);
  transition: color 0.2s var(--ease-out);
  white-space: nowrap;
}

.book-card-mini__cta::after {
  content: '→';
  display: inline-block;
  margin-left: 3px;
  transition: transform 0.2s var(--ease-out);
}

.book-card-mini:hover .book-card-mini__cta::after {
  transform: translateX(3px);
}

/* ---------- Douban rating badge ---------- */
.douban-badge {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 3px 9px 3px 7px;
  border-radius: 999px;
  background: #fff8e6;
  border: 1px solid #f5d77a;
  color: #856404;
  font-size: 0.78rem;
  font-weight: 500;
  text-decoration: none;
  transition: all 0.2s ease;
  line-height: 1.4;
  font-feature-settings: "tnum";
}

.douban-badge svg { color: #2dc26b; flex-shrink: 0; }

/* ---------- Brand marks (logos inside badges) ---------- */
.brand-mark {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  line-height: 1;
}

/* 豆瓣 Douban: green rounded square with 豆 character */
.brand-mark--douban {
  width: 14px;
  height: 14px;
  border-radius: 3px;
  background: #2dc26b;
  color: #fff;
  font-family: var(--font-serif);
  font-weight: 700;
  font-size: 9.5px;
  /* Optical centering for the 豆 glyph */
  padding-top: 1px;
}

/* GitHub Octocat — color follows badge state via currentColor */
.brand-mark--github {
  width: 13px;
  height: 13px;
}

/* When .gh-stars is in "brand" variant (book card), the octocat
   uses the loaded color directly instead of the plain star. */
.gh-stars--brand .brand-mark--github { color: #57606a; }
.gh-stars--brand.loaded .brand-mark--github { color: #1f2328; }
.gh-stars--brand.failed { display: none; }

.douban-badge strong {
  color: #1b1b1b;
  font-weight: 700;
  font-size: 0.82rem;
}

a.douban-badge:hover {
  background: #fef0c5;
  border-color: #e8b948;
  border-bottom-color: #e8b948;
  color: #6b4f00;
  transform: translateY(-1px);
}

.douban-badge--lg {
  padding: 6px 14px 6px 12px;
  font-size: 0.88rem;
  margin-bottom: 18px;
}

.douban-badge--lg strong { font-size: 1.05rem; }
.douban-badge--lg svg { width: 14px; height: 14px; }

/* ---------- Book detail page ---------- */
.book-hero {
  display: flex;
  gap: 48px;
  align-items: flex-start;
  margin: 8px 0 56px;
  padding: 40px 44px;
  background: linear-gradient(135deg, #ffffff 0%, #faf8f3 100%);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-lg);
  position: relative;
  overflow: hidden;
}

.book-hero::before {
  content: '';
  position: absolute;
  top: -120px;
  right: -120px;
  width: 380px;
  height: 380px;
  background:
    radial-gradient(circle at 30% 30%, rgba(30, 64, 175, 0.10) 0%, transparent 60%),
    radial-gradient(circle at 70% 70%, rgba(59, 130, 246, 0.07) 0%, transparent 60%);
  pointer-events: none;
  filter: blur(8px);
}

.book-hero__cover {
  width: 200px;
  flex-shrink: 0;
  position: relative;
  z-index: 1;
  aspect-ratio: 600 / 848;
}

.book-hero__cover img {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  border-radius: var(--radius-sm);
  box-shadow: var(--shadow-book);
  transform: rotate(-2deg);
  transition: transform 0.5s cubic-bezier(0.4, 0, 0.2, 1);
  object-fit: cover;
  display: block;
  z-index: 1;
}

.book-hero__cover .cover-placeholder {
  transform: rotate(-2deg);
}

.book-hero:hover .book-hero__cover img,
.book-hero:hover .book-hero__cover .cover-placeholder {
  transform: rotate(0deg) scale(1.03);
}

.book-hero__meta {
  flex: 1;
  min-width: 0;
  position: relative;
  z-index: 1;
}

.book-hero__meta h1 {
  font-size: 2.2rem;
  margin: 6px 0 8px;
  line-height: 1.2;
}

.book-hero__subtitle {
  font-size: 1.05rem;
  color: var(--color-text-soft);
  margin: 0 0 14px;
  font-family: var(--font-serif);
}

.book-hero__byline {
  font-size: 0.9rem;
  color: var(--color-text-muted);
  margin: 0 0 16px;
}

.book-hero__byline .sep {
  margin: 0 8px;
  color: var(--color-border-strong);
}

.book-hero__blurb {
  font-size: 1rem;
  color: var(--color-text-soft);
  line-height: 1.75;
  margin: 0 0 20px;
}

.archive-note {
  padding: 14px 20px;
  background: var(--color-bg-section);
  border-radius: var(--radius-sm);
  border-left: 3px solid var(--color-border-strong);
  font-size: 0.92rem;
}

.archive-note p { margin: 0; }

/* ---------- Exercises index ---------- */
.exercises-index { margin: 24px 0 48px; }

.exercises-book {
  margin-bottom: 36px;
  padding: 24px 28px;
  background: var(--color-bg-pure);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
}

.exercises-book__head h2 {
  margin: 0 0 6px;
  font-size: 1.3rem;
  border: none;
  padding: 0;
}

.exercises-book__head h2::after { display: none; }

.exercises-book__head p {
  margin: 0 0 16px;
  color: var(--color-text-muted);
  font-size: 0.92rem;
}

.exercises-list {
  list-style: none;
  padding: 0;
  margin: 0;
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 10px;
}

.exercises-list li {
  margin: 0;
  display: flex;
  align-items: center;
  gap: 10px;
  flex-wrap: wrap;
}

.exercises-list a {
  flex: 1;
  display: flex;
  align-items: baseline;
  gap: 10px;
  padding: 10px 14px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  color: var(--color-text);
  text-decoration: none;
  transition: border-color 0.18s var(--ease-out),
              background 0.18s var(--ease-out),
              transform 0.18s var(--ease-out);
  min-width: 0;
}

.exercises-list a:hover {
  border-color: var(--color-border-strong);
  background: var(--color-bg-section);
  color: var(--color-text);
  transform: translateX(2px);
}

.ex-chapter {
  font-family: var(--font-serif);
  font-weight: 700;
  color: var(--color-accent);
  font-size: 0.85rem;
  flex-shrink: 0;
}

.ex-title {
  font-size: 0.94rem;
  flex: 1;
  min-width: 0;
}

.ex-tags em {
  display: inline-block;
  font-style: normal;
  font-size: 0.7rem;
  padding: 2px 6px;
  margin-left: 4px;
  background: var(--color-bg-section);
  border-radius: 3px;
  color: var(--color-text-muted);
}

.exercises-empty {
  margin: 0;
  padding: 16px;
  text-align: center;
  color: var(--color-text-muted);
  font-size: 0.92rem;
  background: var(--color-bg-section);
  border-radius: var(--radius-sm);
}

/* ---------- Viz detail pages (figure grid, captions, legend, attribution) ---------- */
.viz-back {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  color: var(--color-text-muted);
  font-size: 0.88rem;
  text-decoration: none;
  margin-bottom: 24px;
  padding: 4px 0;
  transition: color 0.2s var(--ease-out), gap 0.2s var(--ease-out);
}

.viz-back::before {
  content: '←';
  transition: transform 0.2s var(--ease-out);
}

.viz-back:hover {
  color: var(--color-accent);
  border-bottom-color: transparent;
}

.viz-back:hover::before {
  transform: translateX(-2px);
}

.figure-grid {
  display: grid;
  gap: 22px;
  margin: 24px 0 32px;
}

.figure-grid--2col {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

@media (max-width: 640px) {
  .figure-grid--2col { grid-template-columns: 1fr; }
}

.viz-figure {
  margin: 0;
  padding: 18px 18px 14px;
  background: var(--color-bg-pure);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
  display: flex;
  flex-direction: column;
  align-items: center;
}

.viz-figure img {
  width: 100%;
  height: auto;
  max-width: 360px;
  border-radius: var(--radius-sm);
  background: var(--color-bg-section);
}

.viz-figure--wide {
  padding: 24px;
  margin: 24px 0 16px;
}

.viz-figure--wide img {
  max-width: 100%;
}

.viz-figure figcaption {
  margin-top: 12px;
  font-size: 0.9rem;
  color: var(--color-text-soft);
  text-align: center;
  line-height: 1.5;
}

.viz-figure figcaption code {
  font-size: 0.82rem;
  padding: 1px 6px;
  background: var(--color-bg-section);
  border-radius: 3px;
  color: var(--color-text);
}

.viz-figure__source {
  display: block;
  margin-top: 6px;
  font-size: 0.76rem;
  color: var(--color-text-muted);
  text-align: center;
  line-height: 1.45;
}

.viz-figure__source a {
  color: var(--color-text-muted);
  border-bottom: 1px dotted currentColor;
}

.viz-figure__source a:hover {
  color: var(--color-accent);
  border-bottom-color: var(--color-accent);
}

.viz-legend {
  display: flex;
  flex-wrap: wrap;
  gap: 8px 18px;
  margin: 16px 0 24px;
  padding: 12px 18px;
  background: var(--color-bg-section);
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  color: var(--color-text-soft);
}

.viz-legend code {
  background: transparent;
  border: none;
  padding: 0;
  margin-right: 4px;
  color: var(--color-accent);
  font-weight: 600;
}

.viz-attr {
  font-size: 0.85rem;
  color: var(--color-text-muted);
  margin: 8px 0 28px;
  padding-left: 12px;
  border-left: 2px solid var(--color-border-strong);
}

.viz-attr a { color: var(--color-text-soft); }

/* ---------- Viz grid (Visualization landing page) ---------- */
.viz-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 20px;
  margin: 24px 0 40px;
}

/* Wider page only on the visualization section. */
.viz-page .wrapper { max-width: 1320px; }

/* Responsive collapse: 4 → 3 → 2 → 1 */
@media (max-width: 1100px) {
  .viz-grid { grid-template-columns: repeat(3, 1fr); }
}
@media (max-width: 820px) {
  .viz-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 520px) {
  .viz-grid { grid-template-columns: 1fr; }
}

.viz-card {
  display: flex;
  flex-direction: column;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-bg-pure);
  text-decoration: none;
  color: inherit;
  overflow: hidden;
  transition: transform 0.25s var(--ease-out),
              box-shadow 0.25s var(--ease-out),
              border-color 0.25s var(--ease-out);
}

.viz-card:hover {
  border-color: var(--color-border-strong);
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
  text-decoration: none;
}

.viz-card__thumb {
  aspect-ratio: 16 / 10;
  background: var(--color-bg-section);
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  border-bottom: 1px solid var(--color-border);
  position: relative;
}

.viz-card__thumb img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  object-position: center;
  display: block;
  position: relative;
  z-index: 1;
  transition: transform 0.5s var(--ease-out);
}

.viz-thumb-placeholder {
  position: absolute;
  inset: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 12px;
  background: linear-gradient(135deg, var(--color-bg-section), var(--color-bg-pure));
  color: var(--color-text-soft);
  font-family: var(--font-serif);
  font-size: 0.95rem;
  text-align: center;
  z-index: 0;
}

.viz-thumb-placeholder svg {
  width: 32px;
  height: 32px;
  opacity: 0.6;
}

.viz-card:hover .viz-card__thumb img {
  transform: scale(1.04);
}

.viz-card__body {
  padding: 14px 16px 16px;
  display: flex;
  flex-direction: column;
  gap: 4px;
}

.viz-card__body h3 {
  margin: 0;
  font-family: var(--font-serif);
  font-size: 1rem;
  line-height: 1.35;
  color: var(--color-text);
  transition: color 0.2s var(--ease-out);
  display: -webkit-box;
  -webkit-line-clamp: 1;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.viz-card:hover .viz-card__body h3 {
  color: var(--color-accent);
}

.viz-card__body p {
  margin: 0;
  font-size: 0.85rem;
  color: var(--color-text-muted);
  line-height: 1.5;
  /* Clamp to 3 lines so all cards have identical body height. */
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
  min-height: calc(3 * 1.5 * 0.85rem);
}

/* ---------- Resource grid ---------- */
.resource-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 18px;
  margin: 28px 0 36px;
}

.resource-card {
  display: flex;
  flex-direction: column;
  gap: 6px;
  padding: 22px 24px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  text-decoration: none;
  color: inherit;
  background: var(--color-bg-pure);
  transition: transform 0.25s var(--ease-out),
              box-shadow 0.25s var(--ease-out),
              border-color 0.25s var(--ease-out);
  position: relative;
  overflow: hidden;
}

.resource-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: linear-gradient(90deg, var(--color-accent), var(--color-accent-light));
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.35s var(--ease-out);
}

.resource-card:hover {
  border-color: var(--color-border-strong);
  text-decoration: none;
  transform: translateY(-2px);
  box-shadow: var(--shadow-lg);
}

.resource-card:hover::before { transform: scaleX(1); }

.resource-card h3 {
  margin: 0;
  color: var(--color-text);
  font-size: 1.08rem;
  font-family: var(--font-serif);
  font-weight: 700;
  letter-spacing: -0.005em;
  transition: color 0.2s var(--ease-out);
}

.resource-card:hover h3 { color: var(--color-accent); }

.resource-card p {
  margin: 0;
  color: var(--color-text-muted);
  font-size: 0.92rem;
  line-height: 1.6;
}

/* Non-interactive variant used by "反馈与勘误": no card-level hover, links live inside */
.resource-card--list {
  cursor: default;
}

.resource-card--list:hover {
  transform: none;
  box-shadow: none;
  border-color: var(--color-border);
}

.resource-card--list:hover::before { transform: scaleX(0); }

/* Chip grid used by "反馈与勘误": one row per book, repo+star chip on right. */
.repo-chip-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 8px;
  margin-top: 6px;
}

.repo-chip {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 9px 14px;
  background: var(--color-bg-section);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  text-decoration: none;
  color: var(--color-text);
  font-size: 0.88rem;
  transition: border-color 0.2s var(--ease-out), background 0.2s var(--ease-out), transform 0.2s var(--ease-out);
}

.repo-chip:hover {
  border-color: var(--color-border-strong);
  background: var(--color-bg-pure);
  color: var(--color-accent);
  text-decoration: none;
  transform: translateY(-1px);
}

.repo-chip__title {
  font-weight: 500;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  min-width: 0;
}

.repo-chip__repo {
  flex-shrink: 0;
  font-size: 0.78rem;
  color: var(--color-text-muted);
  background: none;
  padding: 0;
  font-feature-settings: "tnum";
  transition: color 0.2s var(--ease-out);
}

.repo-chip:hover .repo-chip__repo { color: var(--color-accent); }

/* ---------- Footer ---------- */
.site-footer {
  border-top: 1px solid var(--color-border);
  padding: 36px 0 40px;
  color: var(--color-text-muted);
  font-size: 0.88rem;
  text-align: center;
  background: var(--color-bg-section);
  margin-top: 80px;
  position: relative;
}

.site-footer::before {
  content: '';
  position: absolute;
  top: -1px;
  left: 50%;
  transform: translateX(-50%);
  width: 80px;
  height: 2px;
  background: linear-gradient(90deg, transparent, var(--color-accent), transparent);
  opacity: 0.4;
}

.site-footer a {
  color: var(--color-text-muted);
  border-bottom: 1px dotted transparent;
}
.site-footer a:hover { color: var(--color-text); border-bottom-color: currentColor; }
.site-footer p { margin: 0; }
.site-footer .sep {
  display: inline-block;
  margin: 0 10px;
  color: var(--color-border-strong);
}

/* ---------- Mobile ---------- */
@media (max-width: 900px) {
  .book-grid { grid-template-columns: 1fr; gap: 18px; }
}

@media (max-width: 720px) {
  html { font-size: 16px; }
  .wrapper { padding: 0 22px; }
  .site-header .wrapper {
    height: auto;
    padding-top: 14px;
    padding-bottom: 14px;
  }
  .site-nav {
    gap: 14px 18px;
    margin-top: 10px;
    flex-wrap: wrap;
  }
  .site-nav a { font-size: 0.88rem; }
  .site-content { padding: 36px 0 60px; }
  h1 { font-size: 2.1rem; }
  h2 { font-size: 1.4rem; }
  h2::after { width: 36px; }
  .home-hero h1 { font-size: 1.9rem; }
  .book-card {
    flex-direction: column;
    padding: 32px 24px;
    gap: 28px;
  }
  .book-card img {
    width: 170px;
    align-self: center;
    transform: rotate(-1deg);
  }
  .book-card-mini {
    flex-direction: column;
    align-items: center;
    text-align: center;
    padding: 20px;
  }
  .book-card-mini__cover { width: 140px; align-self: center; }
  .book-card-mini__body { width: 100%; align-items: center; }
  .book-card-mini__foot { justify-content: center; }
  .book-hero {
    flex-direction: column;
    padding: 28px 22px;
    gap: 24px;
  }
  .book-hero__cover {
    width: 170px;
    align-self: center;
  }
  .book-hero__meta { text-align: center; }
  .book-hero__meta h1 { font-size: 1.7rem; }
  .book-hero__byline { justify-content: center; }
  .btn-row { justify-content: center; }
}