/* ============================================================
   md2HTML — Minimal Design System
   Line-based · Black/White · Inter + JetBrains Mono
   Reused from parent project's design system
   ============================================================ */

/* ============================================================
   Design Tokens
   ============================================================ */
:root {
  --bg:          #ffffff;
  --bg-soft:     #fafafa;
  --bg-elev:     #ffffff;
  --ink:         #111111;
  --ink-2:       #1a1a1a;
  --ink-soft:    #555555;
  --muted:       #888888;
  --muted-2:     #aaaaaa;
  --line:        #e5e5e5;
  --line-2:      #d0d0d0;
  --accent:      #111111;
  --accent-soft: #555555;
  --accent-ink:  #ffffff;
  --code-bg:     #1a1a1a;
  --code-ink:    #e8e8e8;
  --code-dim:    #777777;
  --code-line:   #2a2a2a;
  --sans: "Inter", -apple-system, BlinkMacSystemFont, "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  --mono: "JetBrains Mono", "SF Mono", Menlo, Consolas, "Noto Sans Mono CJK SC", monospace;
  --text-xs:   12px;
  --text-sm:   14px;
  --text-base: 16px;
  --text-lg:   18px;
  --text-xl:   20px;
  --text-2xl:  24px;
  --text-3xl:  30px;
  --text-4xl:  40px;
  --text-5xl:  56px;
  --weight-normal:   400;
  --weight-medium:   500;
  --weight-semibold: 600;
  --leading-tight:   1.2;
  --leading-normal:  1.6;
  --leading-relaxed: 1.75;
  --space-1:  4px;
  --space-2:  8px;
  --space-3:  12px;
  --space-4:  16px;
  --space-5:  24px;
  --space-6:  32px;
  --space-7:  48px;
  --space-8:  64px;
  --space-9:  96px;
  --space-10: 128px;
  --maxw:   1200px;
  --gutter: 24px;
  --base-size:  16px;
  --prose-size: 16px;
  --prose-lead: 1.75;
}

@media (min-width: 768px) {
  :root { --gutter: 48px; }
}

/* ============================================================
   Dark Theme
   ============================================================ */
[data-theme="dark"] {
  --bg:          #0a0a0a;
  --bg-soft:     #141414;
  --bg-elev:     #1a1a1a;
  --ink:         #eeeeee;
  --ink-2:       #e0e0e0;
  --ink-soft:    #999999;
  --muted:       #666666;
  --muted-2:     #444444;
  --line:        #2a2a2a;
  --line-2:      #333333;
  --accent:      #ffffff;
  --accent-soft: #aaaaaa;
  --accent-ink:  #0a0a0a;
  --code-bg:     #0f0f0f;
  --code-ink:    #e8e8e8;
  --code-dim:    #666666;
  --code-line:   #222222;
}

/* Size Toggle */
[data-size="s"] { --base-size: 15px; --prose-size: 15px; }
[data-size="m"] { --base-size: 16px; --prose-size: 16px; }
[data-size="l"] { --base-size: 18px; --prose-size: 18px; --prose-lead: 1.8; }

/* ============================================================
   Reset & Base
   ============================================================ */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; scroll-padding-top: 72px; }

body {
  font-family: var(--sans);
  font-size: var(--base-size);
  line-height: var(--leading-relaxed);
  color: var(--ink-2);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  transition: background 0.25s ease, color 0.25s ease;
}

::selection {
  background: rgba(100, 180, 255, 0.35);
  color: inherit;
}

pre ::selection,
pre::selection {
  background: rgba(100, 180, 255, 0.35);
  color: inherit;
}

/* ============================================================
   Progress Bar
   ============================================================ */
.progress-bar {
  position: fixed;
  top: 0;
  left: 0;
  height: 2px;
  width: 0%;
  background: var(--ink);
  z-index: 200;
  transition: width 0.1s linear;
}

/* ============================================================
   Top Navigation
   ============================================================ */
.topnav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: color-mix(in srgb, var(--bg) 92%, transparent);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid transparent;
  transition: border-color 0.2s ease;
}
.topnav.scrolled { border-bottom-color: var(--line); }
.topnav-inner {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 0 var(--gutter);
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: center;
  gap: var(--space-6);
  height: 60px;
}
.brand {
  display: flex;
  align-items: baseline;
  gap: var(--space-2);
  text-decoration: none;
  color: var(--ink);
  font-family: var(--sans);
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  border: 0;
  transition: color 0.15s ease;
}
.brand:hover { color: var(--ink-soft); background: transparent; }
.nav-links {
  display: flex;
  gap: 0;
  align-items: center;
  font-family: var(--mono);
  font-size: var(--text-xs);
  letter-spacing: 0.04em;
  text-transform: uppercase;
}
.nav-links a {
  color: var(--muted);
  text-decoration: none;
  padding: var(--space-2) var(--space-4);
  border: 0;
  border-bottom: 2px solid transparent;
  transition: color 0.15s ease, border-color 0.15s ease;
}
.nav-links a:hover { color: var(--ink); background: transparent; }
.nav-links a.active {
  color: var(--ink);
  font-weight: var(--weight-semibold);
  border-bottom-color: var(--ink);
}
.nav-controls {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-left: var(--space-3);
}
.nav-btn {
  appearance: none;
  background: transparent;
  border: 1px solid var(--line-2);
  color: var(--ink-soft);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  padding: 6px 10px;
  cursor: pointer;
  transition: border-color 0.15s ease, color 0.15s ease;
  border-radius: 2px;
  min-width: 44px;
  min-height: 32px;
  display: flex;
  align-items: center;
  justify-content: center;
}
.nav-btn:hover { border-color: var(--ink); color: var(--ink); }
.nav-btn.active { border-color: var(--ink); color: var(--ink); font-weight: var(--weight-medium); }

/* ============================================================
   Layout
   ============================================================ */
.wrap-wide {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 0 var(--gutter);
}
.with-sidebar {
  display: grid;
  grid-template-columns: 240px 1fr;
  max-width: var(--maxw);
  margin: 0 auto;
  min-height: calc(100vh - 60px);
  gap: 0;
}

/* ============================================================
   Sidebar
   ============================================================ */
.sidebar {
  position: sticky;
  top: 60px;
  align-self: start;
  padding: var(--space-7) var(--space-6) var(--space-7) var(--gutter);
  border-right: 1px solid var(--line);
  max-height: calc(100vh - 60px);
  overflow-y: auto;
  background: var(--bg);
}
.sidebar .chapter-num {
  font-family: var(--mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: var(--muted);
  text-transform: uppercase;
  margin-bottom: var(--space-1);
}
.sidebar .chapter-name {
  font-family: var(--sans);
  font-size: var(--text-xl);
  font-weight: var(--weight-medium);
  line-height: var(--leading-tight);
  margin-bottom: var(--space-6);
  color: var(--ink);
}
.sidebar h4 {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--muted);
  font-weight: var(--weight-medium);
  margin-bottom: var(--space-4);
  padding-bottom: var(--space-3);
  border-bottom: 1px solid var(--line);
}
.sidebar ul {
  list-style: none;
  font-size: var(--text-sm);
  line-height: 1.45;
  padding: 0;
  margin: 0;
  counter-reset: toc;
}
.sidebar li { counter-increment: toc; padding: 0; margin: 0; }
.sidebar li::before { display: none; }
.sidebar li a {
  display: grid;
  grid-template-columns: 24px 1fr;
  padding: var(--space-2) 0;
  color: var(--ink-soft);
  text-decoration: none;
  transition: color 0.15s ease;
  border: 0;
}
.sidebar li a::before {
  content: counter(toc, decimal-leading-zero);
  font-family: var(--mono);
  font-size: 10px;
  color: var(--muted-2);
  letter-spacing: 0.04em;
  padding-top: 3px;
}
.sidebar li a:hover { color: var(--ink); background: transparent; }
.sidebar li a.active { color: var(--ink); font-weight: var(--weight-medium); }
.sidebar li a.active::before { color: var(--ink); }

/* ============================================================
   Chapter Body
   ============================================================ */
.chapter-body {
  padding: var(--space-8) var(--space-8) var(--space-10);
  max-width: 760px;
  width: 100%;
  counter-reset: section;
}
article { display: block; }

/* ============================================================
   Typography
   ============================================================ */
h1, h2, h3, h4 {
  font-family: var(--sans);
  color: var(--ink);
  letter-spacing: -0.02em;
}
h1 {
  font-size: clamp(var(--text-4xl), 5vw, var(--text-5xl));
  line-height: 1.08;
  letter-spacing: -0.03em;
  font-weight: var(--weight-semibold);
}
h2 {
  font-size: var(--text-3xl);
  line-height: var(--leading-tight);
  margin: var(--space-9) 0 var(--space-5);
  padding-top: var(--space-5);
  border-top: 1px solid var(--line);
  font-weight: var(--weight-medium);
  counter-increment: section;
}
.chapter-body h2::before {
  content: counter(section, decimal-leading-zero) "  ";
  font-family: var(--mono);
  font-size: var(--text-sm);
  font-weight: var(--weight-normal);
  color: var(--muted);
  letter-spacing: 0.06em;
}
h3 {
  font-size: var(--text-xl);
  line-height: 1.35;
  margin: var(--space-7) 0 var(--space-4);
  font-weight: var(--weight-medium);
  letter-spacing: -0.01em;
}
h4 {
  font-size: var(--text-xs);
  font-family: var(--mono);
  margin: var(--space-6) 0 var(--space-3);
  font-weight: var(--weight-medium);
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
}
p {
  margin: 0 0 var(--space-5);
  color: var(--ink-2);
}
article p {
  font-size: var(--prose-size);
  line-height: var(--prose-lead);
  font-family: var(--sans);
  color: var(--ink-2);
}
a {
  color: var(--ink);
  text-decoration: none;
  border-bottom: 1px solid var(--line-2);
  padding-bottom: 1px;
  transition: border-color 0.15s ease, color 0.15s ease;
}
a:hover { border-bottom-color: var(--ink); }
strong { font-weight: var(--weight-semibold); color: var(--ink); }
em { font-style: italic; color: var(--ink); }
hr { border: 0; height: 1px; background: var(--line); margin: var(--space-8) 0; }

ul, ol { padding-left: 0; margin: 0 0 var(--space-5); list-style: none; }
article ul, article ol {
  font-family: var(--sans);
  font-size: var(--prose-size);
  line-height: var(--prose-lead);
}
ul li, ol li {
  position: relative;
  padding-left: var(--space-5);
  margin-bottom: var(--space-3);
  color: var(--ink-2);
}
ul li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.75em;
  width: 12px;
  height: 1px;
  background: var(--muted);
}
ol { counter-reset: ol-counter; }
ol > li { counter-increment: ol-counter; padding-left: var(--space-7); }
ol > li::before {
  content: counter(ol-counter, decimal-leading-zero);
  position: absolute;
  left: 0;
  top: 2px;
  font-family: var(--mono);
  font-size: var(--text-xs);
  color: var(--muted);
  letter-spacing: 0.04em;
}
blockquote {
  margin: var(--space-6) 0;
  padding: var(--space-2) 0 var(--space-2) var(--space-5);
  border-left: 2px solid var(--line-2);
  color: var(--ink-soft);
  font-style: italic;
  font-family: var(--sans);
  font-size: var(--text-lg);
  line-height: var(--leading-normal);
}

/* ============================================================
   Inline Code & Pre
   ============================================================ */
code {
  font-family: var(--mono);
  font-size: 0.86em;
  background: var(--bg-soft);
  color: var(--ink);
  padding: 2px 6px;
  border: 1px solid var(--line);
  border-radius: 3px;
  white-space: nowrap;
}
pre {
  background: var(--code-bg);
  color: var(--code-ink);
  padding: 36px var(--space-5) var(--space-5);
  overflow-x: auto;
  font-family: var(--mono);
  font-size: 13px;
  line-height: 1.7;
  margin: var(--space-6) 0;
  position: relative;
  border: 1px solid var(--code-line);
  border-radius: 4px;
}
pre[data-label]::before {
  content: attr(data-label);
  position: absolute;
  top: 0;
  left: 0;
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.12em;
  color: var(--code-dim);
  text-transform: uppercase;
  padding: var(--space-2) var(--space-3);
  border-bottom: 1px solid var(--code-line);
  border-right: 1px solid var(--code-line);
}
pre code {
  background: none;
  color: inherit;
  padding: 0;
  border: 0;
  font-size: inherit;
  white-space: pre;
}
pre code.hljs {
  background: transparent;
  padding: 0;
  color: var(--code-ink);
}
.copy-btn {
  position: absolute;
  top: var(--space-2);
  right: var(--space-2);
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--code-dim);
  background: transparent;
  border: 1px solid var(--code-line);
  padding: 4px 10px;
  cursor: pointer;
  opacity: 0;
  transition: opacity 0.15s ease, color 0.15s ease, border-color 0.15s ease, background 0.15s ease;
  border-radius: 3px;
}
pre:hover .copy-btn { opacity: 0.6; }
pre:hover .copy-btn:hover { opacity: 1; color: var(--code-ink); border-color: var(--code-ink); background: var(--code-line); }
.copy-btn.copied { color: #4ade80; border-color: #4ade80; }

/* ============================================================
   Callouts
   ============================================================ */
.callout {
  border: 1px solid var(--line);
  border-left: 3px solid var(--ink);
  padding: var(--space-5);
  margin: var(--space-6) 0;
  background: var(--bg);
  position: relative;
}
.callout-title {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--ink);
  margin: 0 0 var(--space-3);
  font-weight: var(--weight-semibold);
}
.callout p { margin-bottom: var(--space-3); font-family: var(--sans); font-size: var(--text-base); line-height: var(--leading-normal); }
.callout p:last-child { margin-bottom: 0; }
.callout-tip { border-left-color: var(--ink-soft); }
.callout-tip .callout-title { color: var(--ink-soft); }
.callout-warn { border-left-color: var(--ink); }
.callout-warn .callout-title { color: var(--ink); }
.callout-warn .callout-title::after { content: " ⚠"; font-family: var(--sans); }

/* ============================================================
   Tables
   ============================================================ */
.table-wrap {
  overflow-x: auto;
  margin: var(--space-6) 0;
  border: 1px solid var(--line);
  border-radius: 3px;
}
table { width: 100%; border-collapse: collapse; font-family: var(--sans); font-size: var(--text-sm); }
th, td {
  text-align: left;
  padding: var(--space-3) var(--space-4);
  border-bottom: 1px solid var(--line);
  vertical-align: top;
  line-height: 1.55;
}
th {
  font-weight: var(--weight-medium);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  border-bottom: 1px solid var(--line-2);
  background: var(--bg-soft);
}
tr:last-child td { border-bottom: 0; }
td { color: var(--ink-2); }
td code { font-size: 12px; }

/* ============================================================
   Cover / Index Page
   ============================================================ */
.cover {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 0 var(--gutter);
  min-height: calc(100vh - 60px);
}
.cover-hero {
  padding: var(--space-8) 0 var(--space-7);
  border-bottom: 1px solid var(--line);
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-7);
}
.cover-title-block { padding-top: var(--space-3); }
.cover h1 {
  font-size: clamp(36px, 7vw, var(--text-5xl));
  line-height: 1.04;
  letter-spacing: -0.035em;
  font-weight: var(--weight-semibold);
  max-width: 900px;
  color: var(--ink);
}
.cover-lede-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-8);
  padding-top: var(--space-4);
  align-items: start;
}
.cover-lede-row .num {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: var(--space-4);
}
.cover-lede {
  font-family: var(--sans);
  font-size: var(--text-lg);
  line-height: var(--leading-normal);
  color: var(--ink-soft);
  max-width: 540px;
}

/* TOC Grid */
.toc-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 0;
  border-top: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
}
.toc-card {
  display: grid;
  grid-template-rows: auto 1fr auto;
  gap: var(--space-5);
  padding: var(--space-6) var(--space-5);
  text-decoration: none;
  color: var(--ink);
  border-left: 1px solid var(--line);
  min-height: 280px;
  position: relative;
  transition: background 0.2s ease;
  border-bottom: 0;
}
.toc-card:first-child { border-left: 0; }
.toc-card:hover { background: var(--bg-soft); }
.toc-card .num {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.16em;
  color: var(--muted);
  text-transform: uppercase;
  display: flex;
  justify-content: space-between;
  align-items: baseline;
}
.toc-card .num strong {
  font-weight: var(--weight-medium);
  color: var(--ink);
  font-size: var(--text-4xl);
  letter-spacing: -0.02em;
  line-height: 1;
  font-family: var(--sans);
  transition: color 0.2s ease;
}
.toc-card h3 {
  font-size: var(--text-xl);
  line-height: var(--leading-tight);
  letter-spacing: -0.01em;
  font-weight: var(--weight-medium);
  color: var(--ink);
  margin: 0;
}
.toc-card p {
  font-family: var(--sans);
  font-size: var(--text-sm);
  line-height: var(--leading-normal);
  color: var(--ink-soft);
  margin: 0;
}
.toc-card .read {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.12em;
  color: var(--muted);
  text-transform: uppercase;
  display: flex;
  justify-content: space-between;
  padding-top: var(--space-4);
  border-top: 1px solid var(--line);
}

/* ============================================================
   Chapter Head
   ============================================================ */
.chapter-head {
  margin: 0 0 var(--space-8);
  padding-bottom: var(--space-7);
  border-bottom: 1px solid var(--line);
}
.chapter-head-meta {
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
  display: flex;
  justify-content: space-between;
  padding-bottom: var(--space-4);
  margin-bottom: var(--space-5);
  border-bottom: 1px solid var(--line);
}
.chapter-head-meta .num { color: var(--ink); font-weight: var(--weight-medium); }
.chapter-head h1 {
  font-size: clamp(var(--text-3xl), 5vw, var(--text-4xl));
  line-height: 1.1;
  letter-spacing: -0.025em;
  margin: var(--space-3) 0 var(--space-5);
  font-weight: var(--weight-semibold);
}

/* ============================================================
   Pager (prev/next)
   ============================================================ */
.pager {
  display: flex;
  justify-content: space-between;
  margin-top: var(--space-9);
  padding-top: var(--space-6);
  border-top: 1px solid var(--line);
}
.pager a {
  text-decoration: none;
  color: var(--ink);
  border: 0;
  display: grid;
  gap: var(--space-2);
  transition: color 0.15s ease;
}
.pager a:hover { color: var(--ink-soft); }
.pager a:hover .title { text-decoration: underline; }
.pager a:last-child { text-align: right; }
.pager a.next { text-align: right; }
.pager .label {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
}
.pager .title {
  font-family: var(--sans);
  font-size: var(--text-lg);
  letter-spacing: -0.01em;
  font-weight: var(--weight-medium);
  color: var(--ink);
}
.pager a.disabled { opacity: 0.3; pointer-events: none; }

/* ============================================================
   Settings Popover
   ============================================================ */
.settings-pop {
  position: fixed;
  top: 74px;
  right: 20px;
  background: var(--bg-elev);
  border: 1px solid var(--line);
  padding: var(--space-5);
  z-index: 90;
  min-width: 220px;
  display: none;
  box-shadow: 0 12px 36px -12px rgba(0, 0, 0, 0.2);
  border-radius: 4px;
}
.settings-pop.open { display: block; }
.settings-pop h5 {
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: var(--space-2);
  font-weight: var(--weight-medium);
}
.settings-pop .row { display: flex; gap: 6px; margin-bottom: var(--space-3); }
.settings-pop .row:last-child { margin-bottom: 0; }
.settings-pop .seg {
  flex: 1;
  appearance: none;
  background: transparent;
  border: 1px solid var(--line-2);
  color: var(--ink-soft);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.04em;
  padding: 6px 4px;
  cursor: pointer;
  transition: border-color 0.15s ease, color 0.15s ease, background 0.15s ease;
  text-transform: uppercase;
  min-height: 32px;
}
.settings-pop .seg:hover { border-color: var(--ink-soft); color: var(--ink); }
.settings-pop .seg.active { border-color: var(--ink); background: var(--ink); color: var(--bg); }

/* ============================================================
   Collapsible Sections
   ============================================================ */
.collapsible { border-bottom: 1px solid var(--line); }
.collapsible-trigger {
  display: flex;
  align-items: center;
  justify-content: space-between;
  width: 100%;
  padding: var(--space-4) 0;
  background: transparent;
  border: 0;
  cursor: pointer;
  font-family: var(--sans);
  font-size: var(--text-base);
  font-weight: var(--weight-medium);
  color: var(--ink);
  text-align: left;
  min-height: 44px;
}
.collapsible-trigger:hover { color: var(--ink-soft); }
.collapsible-icon {
  width: 16px;
  height: 16px;
  flex-shrink: 0;
  transition: transform 0.2s ease-out;
  color: var(--muted);
}
[aria-expanded="true"] .collapsible-icon { transform: rotate(90deg); }
.collapsible-content { display: grid; grid-template-rows: 0fr; transition: grid-template-rows 0.2s ease-out; }
.collapsible-content:not([hidden]) { grid-template-rows: 1fr; }
.collapsible-inner { overflow: hidden; padding-bottom: var(--space-4); }

/* ============================================================
   Tab Panels
   ============================================================ */
.tabs { margin: var(--space-6) 0; }
.tabs-list {
  display: flex;
  gap: 0;
  border-bottom: 1px solid var(--line);
  margin-bottom: var(--space-5);
}
.tabs-list [role="tab"] {
  appearance: none;
  background: transparent;
  border: 0;
  border-bottom: 2px solid transparent;
  padding: var(--space-3) var(--space-4);
  font-family: var(--sans);
  font-size: var(--text-sm);
  color: var(--muted);
  cursor: pointer;
  transition: color 0.15s ease, border-color 0.15s ease;
  min-height: 44px;
}
.tabs-list [role="tab"]:hover { color: var(--ink); }
.tabs-list [role="tab"][aria-selected="true"] {
  color: var(--ink);
  font-weight: var(--weight-medium);
  border-bottom-color: var(--ink);
}
.tabs [role="tabpanel"] { padding: var(--space-2) 0; }

/* ============================================================
   Search Overlay
   ============================================================ */
.search-backdrop {
  position: fixed;
  inset: 0;
  background: color-mix(in srgb, var(--ink) 50%, transparent);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
  z-index: 500;
  display: none;
  align-items: flex-start;
  justify-content: center;
  padding: var(--space-9) var(--space-6);
}
.search-backdrop:not([hidden]) { display: flex; }
.search-modal {
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: 6px;
  max-width: 600px;
  width: 100%;
  max-height: 70vh;
  overflow: hidden;
  display: flex;
  flex-direction: column;
  box-shadow: 0 24px 64px -16px rgba(0, 0, 0, 0.3);
}
.search-input-wrap {
  display: flex;
  align-items: center;
  padding: var(--space-4) var(--space-5);
  border-bottom: 1px solid var(--line);
  gap: var(--space-3);
}
.search-input {
  flex: 1;
  appearance: none;
  border: 0;
  background: transparent;
  font-family: var(--sans);
  font-size: var(--text-base);
  color: var(--ink);
  outline: none;
}
.search-input::placeholder { color: var(--muted); }
.search-results { overflow-y: auto; padding: var(--space-2); flex: 1; }
.search-result {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: var(--space-3) var(--space-4);
  text-decoration: none;
  color: var(--ink);
  border: 0;
  border-radius: 4px;
  transition: background 0.15s ease;
  min-height: 44px;
}
.search-result:hover { background: var(--bg-soft); }
.search-result-title { font-size: var(--text-sm); font-weight: var(--weight-medium); }
.search-result-chapter {
  font-family: var(--mono);
  font-size: 11px;
  color: var(--muted);
  letter-spacing: 0.04em;
  text-transform: uppercase;
  flex-shrink: 0;
  margin-left: var(--space-4);
}
.search-empty { padding: var(--space-5) var(--space-4); color: var(--muted); font-size: var(--text-sm); text-align: center; }

/* ============================================================
   Mobile TOC
   ============================================================ */
.mtoc-fab {
  display: none;
  position: fixed;
  bottom: var(--space-5);
  right: var(--space-5);
  z-index: 80;
  width: 48px;
  height: 48px;
  border-radius: 50%;
  border: 1px solid var(--line-2);
  background: var(--bg-elev);
  color: var(--ink);
  font-family: var(--mono);
  font-size: 10px;
  letter-spacing: 0.08em;
  cursor: pointer;
  box-shadow: 0 8px 24px -8px rgba(0, 0, 0, 0.2);
  min-width: 48px;
  min-height: 48px;
}
.mtoc-drawer {
  display: none;
  position: fixed;
  inset: 0;
  background: color-mix(in srgb, var(--ink) 50%, transparent);
  backdrop-filter: blur(4px);
  z-index: 300;
  align-items: flex-end;
  justify-content: center;
}
.mtoc-drawer.open { display: flex; }
.mtoc-drawer > div {
  background: var(--bg-elev);
  width: 100%;
  max-width: 560px;
  padding: var(--space-5) var(--space-5) var(--space-6);
  border-top-left-radius: 8px;
  border-top-right-radius: 8px;
  max-height: 80vh;
  overflow-y: auto;
}

/* ============================================================
   Footer
   ============================================================ */
footer {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: var(--space-7) var(--gutter);
  border-top: 1px solid var(--line);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: var(--space-5);
}
footer .set { display: flex; gap: var(--space-5); }

/* kbd */
kbd {
  font-family: var(--mono);
  font-size: 0.82em;
  padding: 2px 7px;
  background: var(--bg-soft);
  border: 1px solid var(--line-2);
  border-bottom-width: 2px;
  border-radius: 3px;
  color: var(--ink);
  white-space: nowrap;
  box-shadow: 0 1px 0 rgba(0, 0, 0, 0.04);
}
[data-theme="dark"] kbd { background: var(--bg-soft); border-color: var(--line-2); box-shadow: 0 1px 0 rgba(0, 0, 0, 0.3); }

/* ============================================================
   Scrollbar
   ============================================================ */
::-webkit-scrollbar { width: 8px; height: 8px; }
::-webkit-scrollbar-track { background: var(--bg); }
::-webkit-scrollbar-thumb { background: var(--line-2); border-radius: 8px; }
::-webkit-scrollbar-thumb:hover { background: var(--muted); }

/* ============================================================
   Responsive
   ============================================================ */
@media (max-width: 1100px) {
  :root { --gutter: 32px; }
  .toc-grid { grid-template-columns: repeat(2, 1fr); }
  .cover-lede-row { grid-template-columns: 1fr; gap: var(--space-6); }
}

@media (max-width: 768px) {
  :root { --gutter: 20px; }
  .with-sidebar { grid-template-columns: 1fr; }
  .sidebar { display: none; }
  .mtoc-fab { display: flex; align-items: center; justify-content: center; }
  .chapter-body { padding: var(--space-6) var(--gutter) var(--space-8); }
  .toc-grid { grid-template-columns: 1fr; }
  .toc-card { min-height: auto; border-left: 0; border-bottom: 1px solid var(--line); }
  .topnav-inner { grid-template-columns: auto auto; gap: var(--space-3); }
  .nav-links { display: none; }
  .cover h1 { font-size: var(--text-3xl); }
  .pager { flex-direction: column; gap: var(--space-5); }
  .pager a.next { text-align: left; }
}