:root {
  --color-surface: #f7f7f7;
  --color-surface-alt: #eeeeee;
  --color-surface-deep: #e1e2e2;
  --color-ink: #414949;
  --color-ink-soft: #636e6e;
  --color-ink-muted: #7a8585;
  --color-line: #d6d8d8;
  --color-primary: #0c8083;
  --color-primary-ink: #ffffff;
  --color-primary-soft: #d6e6e7;
  --color-accent: #ec0d13;
  --color-accent-ink: #ffffff;
  --color-highlight: #f5cdce;
  --color-focus: #e00106;
  --color-contrast-surface: #0f2021;
  --color-contrast-ink: #e4e7e7;
  --color-contrast-line: #3e4c4d;
  --color-contrast-accent: #f44347;
  --overlay-scrim: linear-gradient(180deg, rgba(15, 32, 33, 0.35) 0%, rgba(15, 32, 33, 0.72) 55%, rgba(15, 32, 33, 0.92) 100%);
  --font-heading: ui-monospace, SFMono-Regular, Menlo, Consolas, "PingFang SC", monospace;
  --font-body: "PingFang SC", "Microsoft YaHei", "Source Han Sans SC", sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --text-xs: 11.4px;
  --text-sm: 14.3px;
  --text-base: 16px;
  --text-lg: 20.0px;
  --text-xl: 25.0px;
  --text-2xl: 31.2px;
  --text-3xl: 39.1px;
  --text-4xl: 48.8px;
  --text-display: clamp(39px, 8.0vw, 103px);
  --text-figure: clamp(33px, 5.8vw, 74px);
  --weight-heading: 632;
  --weight-body: 400;
  --leading-body: 1.71;
  --leading-heading: 1.21;
  --tracking-heading: 0.015em;
  --radius-sm: 167px;
  --radius-md: 351px;
  --radius-lg: 535px;
  --radius-pill: 999px;
  --border-thin: 1px;
  --border-thick: 1px;
  --shadow-1: 0 0 0 1px rgba(236, 13, 19, 0.35);
  --shadow-2: 0 0 28px rgba(236, 13, 19, 0.35);
  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 32px;
  --space-6: 48px;
  --space-8: 64px;
  --container: 1200px;
  --measure: 67ch;
  --gutter: 16px;
  --section-y: 82px;
  --section-y-lg: 115px;
}

/* ==========================================================================
   reset 与中文排版
   ========================================================================== */
*,
*::before,
*::after { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
}

body {
  margin: 0;
  background-color: var(--color-surface);
  color: var(--color-ink);
  font-family: var(--font-body);
  font-size: var(--text-base);
  font-weight: var(--weight-body);
  line-height: var(--leading-body);
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4, h5, h6 {
  margin: 0 0 var(--space-2);
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  line-height: var(--leading-heading);
  letter-spacing: var(--tracking-heading);
  color: var(--color-ink);
  text-wrap: balance;
}

p { margin: 0 0 var(--space-2); }
p:last-child { margin-bottom: 0; }

ul, ol { margin: 0; padding: 0; list-style: none; }

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color 160ms ease-out, background-color 160ms ease-out;
}

a:hover { color: color-mix(in srgb, var(--color-primary) 72%, var(--color-ink)); }

img, svg, picture, video { display: block; max-width: 100%; }

button { font: inherit; color: inherit; }

strong { font-weight: var(--weight-heading); }

:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
}

::selection {
  background-color: var(--color-highlight);
  color: var(--color-ink);
}

/* ==========================================================================
   容器与区块节奏
   ========================================================================== */
.shell {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: var(--gutter);
}

.section { padding-block: var(--section-y); }
.section--lg { padding-block: var(--section-y-lg); }
.section--tight { padding-block: var(--space-6); }

.band {
  width: 100%;
  padding-block: var(--section-y);
}

.band--dark {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  border-top: var(--border-thin) solid var(--color-contrast-line);
  border-bottom: var(--border-thin) solid var(--color-contrast-line);
  box-shadow: inset 0 1px 0 rgba(228, 231, 231, 0.14), inset 0 -1px 0 rgba(228, 231, 231, 0.14);
}

.band--dark h1, .band--dark h2, .band--dark h3, .band--dark h4 { color: var(--color-contrast-ink); }
.band--dark p, .band--dark li { color: color-mix(in srgb, var(--color-contrast-ink) 86%, var(--color-contrast-surface)); }
.band--dark a { color: var(--color-contrast-accent); }

.section__head {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: var(--space-3);
  margin-bottom: var(--space-6);
}

.section__title {
  margin: 0;
  font-size: var(--text-xl);
  letter-spacing: var(--tracking-heading);
}

.chapter-index {
  flex: none;
  font-family: var(--font-mono);
  font-size: var(--text-3xl);
  font-weight: 600;
  line-height: 1;
  letter-spacing: -0.02em;
  color: var(--color-primary);
  font-variant-numeric: tabular-nums;
}

.band--dark .chapter-index { color: var(--color-contrast-accent); }

/* 刻度尺：替代实线的分隔语言 */
.rule-scale {
  display: block;
  width: 100%;
  height: 10px;
  border-radius: var(--radius-pill);
  background-color: var(--color-surface-deep);
  background-image: repeating-linear-gradient(
    90deg,
    color-mix(in srgb, var(--color-ink-muted) 60%, transparent) 0 1px,
    transparent 1px 12px
  );
}

.rule-scale--dark { background-color: var(--color-contrast-line); }

/* ==========================================================================
   面板
   ========================================================================== */
.panel {
  position: relative;
  background-color: var(--color-surface);
  border: var(--border-thin) solid var(--color-line);
  border-radius: calc(var(--space-2) + var(--space-1));
  padding: var(--space-4);
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.72);
}

.panel--dark {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  border-color: var(--color-contrast-line);
  box-shadow: inset 0 1px 0 rgba(228, 231, 231, 0.16);
}

.panel--dark h1, .panel--dark h2, .panel--dark h3, .panel--dark h4 { color: var(--color-contrast-ink); }
.panel--dark p, .panel--dark li { color: color-mix(in srgb, var(--color-contrast-ink) 86%, var(--color-contrast-surface)); }
.panel--dark a { color: var(--color-contrast-accent); }
.panel--dark a:hover { color: var(--color-contrast-ink); }

.panel--flush { padding: 0; overflow: hidden; }

/* ==========================================================================
   按钮与胶囊
   ========================================================================== */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-1);
  padding: 10px 22px;
  border: var(--border-thin) solid transparent;
  border-radius: var(--radius-pill);
  font-family: var(--font-body);
  font-size: var(--text-sm);
  font-weight: 600;
  line-height: 1.2;
  text-align: center;
  cursor: pointer;
  transition: transform 160ms ease-out, box-shadow 160ms ease-out,
              background-color 160ms ease-out, color 160ms ease-out;
}

.btn:hover { transform: translateY(-2px); }

.btn--primary {
  background-color: var(--color-primary);
  color: var(--color-primary-ink);
  border-color: var(--color-primary);
}

.btn--primary:hover {
  color: var(--color-primary-ink);
  background-color: color-mix(in srgb, var(--color-primary) 84%, var(--color-contrast-surface));
  box-shadow: var(--shadow-2);
}

.btn--accent {
  background-color: var(--color-accent);
  color: var(--color-accent-ink);
  border-color: var(--color-accent);
}

.btn--accent:hover {
  color: var(--color-accent-ink);
  background-color: color-mix(in srgb, var(--color-accent) 84%, var(--color-contrast-surface));
}

.btn--ghost {
  background-color: transparent;
  color: var(--color-primary);
  border-color: color-mix(in srgb, var(--color-primary) 55%, transparent);
}

.btn--ghost:hover {
  background-color: var(--color-primary-soft);
  color: var(--color-primary);
  border-color: var(--color-primary);
}

.band--dark .btn--ghost,
.panel--dark .btn--ghost {
  color: var(--color-contrast-ink);
  border-color: var(--color-contrast-line);
}

.band--dark .btn--ghost:hover,
.panel--dark .btn--ghost:hover {
  background-color: color-mix(in srgb, var(--color-contrast-ink) 14%, transparent);
  color: var(--color-contrast-ink);
}

/* 徽标式强调 */
.badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 4px 12px;
  border-radius: var(--radius-pill);
  background-color: var(--color-primary-soft);
  color: var(--color-primary);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  line-height: 1.6;
  white-space: nowrap;
}

.badge--accent {
  background-color: var(--color-highlight);
  color: var(--color-accent);
}

.badge--dark {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}

.band--dark .badge--dark,
.panel--dark .badge--dark {
  background-color: color-mix(in srgb, var(--color-contrast-ink) 16%, transparent);
  color: var(--color-contrast-ink);
}

/* ==========================================================================
   状态条与指示灯
   ========================================================================== */
.status-chip {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  margin: 0;
  padding: 6px 14px;
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-pill);
  background-color: var(--color-surface-alt);
  color: var(--color-ink-soft);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  line-height: 1.6;
  white-space: nowrap;
}

.status-chip--tight { padding: 5px 12px; }

.status-chip__label { white-space: nowrap; }

.status-chip__code {
  padding: 1px 8px;
  border-radius: var(--radius-pill);
  background-color: var(--color-surface-deep);
  color: var(--color-ink-muted);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  font-variant-numeric: tabular-nums;
}

.status-lamp {
  flex: none;
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background-color: var(--color-primary);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--color-primary) 22%, transparent);
  animation: lamp-breathe 2s ease-in-out infinite;
}

.status-lamp--idle {
  background-color: var(--color-ink-muted);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--color-ink-muted) 20%, transparent);
  animation: none;
}

.status-lamp--alert {
  background-color: var(--color-accent);
  box-shadow: 0 0 0 3px color-mix(in srgb, var(--color-accent) 22%, transparent);
}

.band--dark .status-lamp,
.panel--dark .status-lamp { background-color: var(--color-contrast-accent); }

@keyframes lamp-breathe {
  0%, 100% { opacity: 0.85; }
  50% { opacity: 1; }
}

/* ==========================================================================
   页头：居中刊头式导航
   ========================================================================== */
.skip-link {
  position: absolute;
  top: -120px;
  left: var(--space-2);
  z-index: 200;
  padding: 10px 22px;
  border-radius: var(--radius-pill);
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  font-size: var(--text-sm);
  font-weight: 600;
  box-shadow: var(--shadow-2);
}

.skip-link:focus {
  top: var(--space-2);
  color: var(--color-contrast-ink);
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 60;
  background-color: var(--color-surface);
  color: var(--color-ink);
  border-bottom: var(--border-thin) solid var(--color-line);
  transition: box-shadow 160ms ease-out;
}

.site-header[data-condensed] {
  box-shadow: 0 10px 26px rgba(15, 32, 33, 0.14);
}

.header-strip {
  height: 6px;
  background-image:
    repeating-linear-gradient(90deg, rgba(15, 32, 33, 0.5) 0 1px, transparent 1px 14px),
    linear-gradient(90deg, var(--color-primary) 0%, var(--color-accent) 100%);
}

.header-rail {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr);
  align-items: center;
  gap: var(--space-3);
  padding-block: var(--space-3);
  transition: padding 160ms ease-out;
}

.site-header[data-condensed] .header-rail { padding-block: var(--space-1); }

.masthead { text-align: center; }

.masthead__brand {
  display: block;
  font-family: var(--font-heading);
  font-size: var(--text-2xl);
  font-weight: var(--weight-heading);
  letter-spacing: 0.14em;
  line-height: 1.1;
  color: var(--color-ink);
  transition: font-size 160ms ease-out;
}

.masthead__brand:hover { color: var(--color-primary); }

.site-header[data-condensed] .masthead__brand { font-size: var(--text-lg); }

.masthead__sub {
  margin: 6px 0 0;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.16em;
  color: var(--color-ink-muted);
}

.site-header[data-condensed] .masthead__sub { display: none; }

.header-actions {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: var(--space-2);
}

.nav-toggle {
  display: none;
  align-items: center;
  gap: var(--space-1);
  padding: 9px 18px;
  border: var(--border-thin) solid var(--color-primary);
  border-radius: var(--radius-pill);
  background-color: var(--color-surface);
  color: var(--color-primary);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  cursor: pointer;
}

.nav-toggle__bars {
  position: relative;
  display: block;
  width: 16px;
  height: 2px;
  border-radius: 2px;
  background-color: currentColor;
}

.nav-toggle__bars::before,
.nav-toggle__bars::after {
  content: "";
  position: absolute;
  left: 0;
  width: 16px;
  height: 2px;
  border-radius: 2px;
  background-color: currentColor;
}

.nav-toggle__bars::before { top: -5px; }
.nav-toggle__bars::after { top: 5px; }

.site-nav {
  display: block;
  border-top: 1px dotted var(--color-line);
}

.site-nav__list {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: var(--space-1);
  max-width: var(--container);
  margin-inline: auto;
  padding: var(--space-2) var(--gutter);
  transition: padding 160ms ease-out;
}

.site-header[data-condensed] .site-nav__list { padding-block: var(--space-1); }

.nav-pill {
  display: inline-block;
  padding: 9px 20px;
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-pill);
  background-color: var(--color-surface);
  color: var(--color-ink);
  font-size: var(--text-sm);
  line-height: 1.3;
  white-space: nowrap;
  transition: background-color 160ms ease-out, color 160ms ease-out,
              border-color 160ms ease-out, transform 160ms ease-out;
}

.nav-pill:hover {
  transform: translateY(-2px);
  background-color: var(--color-primary-soft);
  border-color: var(--color-primary);
  color: var(--color-primary);
}

.nav-pill[aria-current="page"] {
  background-color: var(--color-primary);
  border-color: var(--color-primary);
  color: var(--color-primary-ink);
  font-weight: 600;
}

.nav-pill[aria-current="page"]:hover {
  background-color: color-mix(in srgb, var(--color-primary) 84%, var(--color-contrast-surface));
  color: var(--color-primary-ink);
}

.site-header[data-condensed] .nav-pill {
  padding: 6px 16px;
  font-size: var(--text-xs);
}

.scroll-meter {
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 2px;
  background-color: var(--color-surface-deep);
  pointer-events: none;
  overflow: hidden;
}

.scroll-meter > span {
  display: block;
  width: 100%;
  height: 100%;
  transform: scaleX(0);
  transform-origin: left center;
  background-image: linear-gradient(90deg, var(--color-primary), var(--color-accent));
}

/* ==========================================================================
   页脚：卡片式面板组
   ========================================================================== */
.site-footer {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  padding-block: var(--section-y) var(--space-4);
  border-top: var(--border-thin) solid var(--color-contrast-line);
  box-shadow: inset 0 1px 0 rgba(228, 231, 231, 0.16);
}

.footer-deck {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: var(--space-3);
}

.footer-card {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  padding: var(--space-4);
  border: var(--border-thin) solid var(--color-contrast-line);
  border-radius: calc(var(--space-2) + var(--space-1));
  background-color: color-mix(in srgb, var(--color-contrast-ink) 5%, var(--color-contrast-surface));
  box-shadow: inset 0 1px 0 rgba(228, 231, 231, 0.18);
}

.footer-card__title {
  margin: 0;
  font-family: var(--font-heading);
  font-size: var(--text-lg);
  font-weight: var(--weight-heading);
  letter-spacing: 0.08em;
  color: var(--color-contrast-ink);
}

.footer-card__meta {
  margin: 0;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: color-mix(in srgb, var(--color-contrast-ink) 62%, var(--color-contrast-surface));
}

.footer-card__text {
  margin: 0;
  font-size: var(--text-sm);
  line-height: 1.7;
  color: color-mix(in srgb, var(--color-contrast-ink) 88%, var(--color-contrast-surface));
}

.footer-card__note {
  margin: 0;
  padding-top: var(--space-2);
  border-top: 1px dotted var(--color-contrast-line);
  font-size: var(--text-xs);
  line-height: 1.7;
  color: color-mix(in srgb, var(--color-contrast-ink) 66%, var(--color-contrast-surface));
}

.footer-list {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.footer-list li {
  display: grid;
  grid-template-columns: 5.5em minmax(0, 1fr);
  gap: var(--space-2);
  align-items: baseline;
}

.footer-list__key {
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: var(--color-contrast-accent);
}

.footer-list__value {
  font-size: var(--text-sm);
  line-height: 1.7;
  color: var(--color-contrast-ink);
  word-break: break-word;
}

.footer-links {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-1);
}

.footer-links a {
  display: inline-block;
  padding: 6px 16px;
  border: var(--border-thin) solid var(--color-contrast-line);
  border-radius: var(--radius-pill);
  color: var(--color-contrast-ink);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  transition: background-color 160ms ease-out, border-color 160ms ease-out, color 160ms ease-out;
}

.footer-links a:hover {
  background-color: color-mix(in srgb, var(--color-contrast-ink) 14%, transparent);
  border-color: var(--color-contrast-accent);
  color: var(--color-contrast-ink);
}

.footer-base {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
  margin-top: var(--space-6);
}

.footer-base__scale {
  display: block;
  width: 100%;
  height: 10px;
  border-radius: var(--radius-pill);
  background-color: var(--color-contrast-line);
  background-image: repeating-linear-gradient(
    90deg,
    color-mix(in srgb, var(--color-contrast-ink) 40%, transparent) 0 1px,
    transparent 1px 12px
  );
}

.footer-base__note {
  margin: 0;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.12em;
  color: color-mix(in srgb, var(--color-contrast-ink) 58%, var(--color-contrast-surface));
}

.site-footer:focus-within .footer-links a:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
}

/* ==========================================================================
   通用内容组件
   ========================================================================== */
.prose {
  max-width: var(--measure);
}

.prose h2 { font-size: var(--text-xl); margin-top: var(--space-6); }
.prose h3 { font-size: var(--text-lg); margin-top: var(--space-4); }
.prose p, .prose li { font-size: var(--text-base); }
.prose ul, .prose ol { padding-left: var(--space-3); }
.prose ul li { list-style: none; position: relative; padding-left: var(--space-2); margin-bottom: var(--space-1); }
.prose ul li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.68em;
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background-color: var(--color-primary);
}
.prose ol { counter-reset: prose-step; }
.prose ol li {
  counter-increment: prose-step;
  position: relative;
  padding-left: var(--space-4);
  margin-bottom: var(--space-2);
}
.prose ol li::before {
  content: counter(prose-step, decimal-leading-zero);
  position: absolute;
  left: 0;
  top: 0.1em;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  color: var(--color-ink-muted);
}

.lede {
  max-width: var(--measure);
  font-size: var(--text-lg);
  line-height: 1.55;
  color: var(--color-ink-soft);
}

.band--dark .lede,
.panel--dark .lede { color: color-mix(in srgb, var(--color-contrast-ink) 82%, var(--color-contrast-surface)); }

/* 展示字号：仅限首屏主标题与超大数字 */
.display-hero {
  margin: 0;
  font-family: var(--font-heading);
  font-size: var(--text-display);
  font-weight: var(--weight-heading);
  line-height: 1.03;
  letter-spacing: -0.02em;
  color: var(--color-contrast-ink);
}

.display-figure {
  display: block;
  font-family: var(--font-mono);
  font-size: var(--text-figure);
  font-weight: 600;
  line-height: 1.05;
  letter-spacing: -0.02em;
  font-variant-numeric: tabular-nums;
  color: var(--color-contrast-accent);
}

/* 栅格 */
.grid {
  display: grid;
  gap: var(--gutter);
}

.grid--2 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.grid--3 { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.grid--4 { grid-template-columns: repeat(4, minmax(0, 1fr)); }
.grid--split { grid-template-columns: minmax(0, 7fr) minmax(0, 5fr); }
.grid--12 { grid-template-columns: repeat(12, minmax(0, 1fr)); }

/* 排列辅助 */
.cluster {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-2);
}

.stack > * + * { margin-top: var(--space-3); }

/* 面包屑 */
.breadcrumb {
  margin-bottom: var(--space-3);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
}

.breadcrumb ol {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-1);
}

.breadcrumb li { display: inline-flex; align-items: center; gap: var(--space-1); }

.breadcrumb li:not(:last-child)::after {
  content: "›";
  color: var(--color-ink-muted);
}

.breadcrumb a { color: var(--color-ink-muted); }
.breadcrumb a:hover { color: var(--color-primary); }
.breadcrumb [aria-current="page"] { color: var(--color-ink); }

/* 胶囊筛选器 */
.chip-filter {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-1);
  padding: var(--space-1);
  border-radius: var(--radius-pill);
  background-color: var(--color-surface-deep);
}

.chip {
  padding: 7px 18px;
  border: var(--border-thin) solid transparent;
  border-radius: var(--radius-pill);
  background-color: transparent;
  color: var(--color-ink-soft);
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  cursor: pointer;
  transition: background-color 160ms ease-out, color 160ms ease-out, border-color 160ms ease-out;
}

.chip:hover {
  background-color: var(--color-primary-soft);
  color: var(--color-ink);
}

.chip[aria-pressed="true"] {
  background-color: var(--color-primary);
  border-color: var(--color-primary);
  color: var(--color-primary-ink);
}

.band--dark .chip-filter,
.panel--dark .chip-filter { background-color: color-mix(in srgb, var(--color-contrast-ink) 8%, transparent); }
.band--dark .chip,
.panel--dark .chip { color: color-mix(in srgb, var(--color-contrast-ink) 70%, var(--color-contrast-surface)); }
.band--dark .chip:hover,
.panel--dark .chip:hover { background-color: color-mix(in srgb, var(--color-contrast-ink) 14%, transparent); color: var(--color-contrast-ink); }
.band--dark .chip[aria-pressed="true"],
.panel--dark .chip[aria-pressed="true"] { background-color: var(--color-contrast-accent); border-color: var(--color-contrast-accent); color: var(--color-contrast-surface); }

/* 折叠面板 */
.fold {
  border: var(--border-thin) solid var(--color-line);
  border-radius: calc(var(--space-2) + var(--space-1));
  background-color: var(--color-surface);
  overflow: hidden;
}

.fold + .fold { margin-top: var(--space-2); }

.fold__trigger {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  width: 100%;
  padding: var(--space-3) var(--space-4);
  border: 0;
  border-bottom: 1px dotted var(--color-line);
  background-color: var(--color-surface-alt);
  color: var(--color-ink);
  font-family: var(--font-heading);
  font-size: var(--text-base);
  font-weight: var(--weight-heading);
  letter-spacing: var(--tracking-heading);
  text-align: left;
  cursor: pointer;
  transition: background-color 160ms ease-out;
}

.fold__trigger:hover { background-color: var(--color-primary-soft); }

.fold__trigger::after {
  content: "+";
  margin-left: auto;
  font-family: var(--font-mono);
  font-size: var(--text-lg);
  line-height: 1;
  color: var(--color-primary);
}

.fold__trigger[aria-expanded="true"]::after { content: "–"; }

.fold__panel {
  padding: var(--space-4);
  font-size: var(--text-base);
  color: var(--color-ink-soft);
}

.fold__panel[hidden] { display: none; }

.band--dark .fold,
.panel--dark .fold {
  background-color: color-mix(in srgb, var(--color-contrast-ink) 5%, var(--color-contrast-surface));
  border-color: var(--color-contrast-line);
}
.band--dark .fold__trigger,
.panel--dark .fold__trigger {
  background-color: color-mix(in srgb, var(--color-contrast-ink) 8%, var(--color-contrast-surface));
  border-bottom-color: var(--color-contrast-line);
  color: var(--color-contrast-ink);
}
.band--dark .fold__trigger:hover,
.panel--dark .fold__trigger:hover { background-color: color-mix(in srgb, var(--color-contrast-ink) 16%, var(--color-contrast-surface)); }
.band--dark .fold__panel,
.panel--dark .fold__panel { color: color-mix(in srgb, var(--color-contrast-ink) 84%, var(--color-contrast-surface)); }

/* 图录式图片容器 */
.figure-frame {
  position: relative;
  display: block;
  width: 100%;
  overflow: hidden;
  border: var(--border-thin) solid var(--color-line);
  border-radius: calc(var(--space-2) + var(--space-1));
  background-color: var(--color-surface-deep);
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.55);
}

.figure-frame--16x9 { aspect-ratio: 16 / 9; }
.figure-frame--1x1 { aspect-ratio: 1 / 1; }

.figure-frame__media,
.figure-frame img,
.figure-frame picture > img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.figure-frame__overlay {
  position: absolute;
  inset: 0;
  background-image: var(--overlay-scrim);
  pointer-events: none;
}

.figure-frame__caption {
  position: absolute;
  left: var(--space-3);
  right: var(--space-3);
  bottom: var(--space-3);
  margin: 0;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  line-height: 1.6;
  color: var(--color-contrast-ink);
}

.figure-frame--dark { border-color: var(--color-contrast-line); background-color: var(--color-contrast-surface); }

/* ==========================================================================
   响应式
   ========================================================================== */
@media (max-width: 1024px) {
  .grid--4 { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .grid--12 { grid-template-columns: repeat(6, minmax(0, 1fr)); }
  .footer-deck { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (max-width: 900px) {
  .header-rail {
    grid-template-columns: minmax(0, 1fr) auto;
    grid-template-areas:
      "brand toggle"
      "status actions";
    row-gap: var(--space-2);
    column-gap: var(--space-2);
  }

  .masthead { grid-area: brand; text-align: left; }
  .masthead__sub { letter-spacing: 0.08em; }
  .nav-toggle { grid-area: toggle; display: inline-flex; }
  .status-chip { grid-area: status; justify-self: start; }
  .header-actions { grid-area: actions; justify-self: end; }

  .site-nav {
    display: none;
    border-top: 1px dotted var(--color-line);
  }

  .site-nav[data-open] { display: block; }

  .site-nav__list {
    flex-direction: column;
    align-items: stretch;
    gap: var(--space-1);
    padding-block: var(--space-2);
  }

  .nav-pill { display: block; text-align: center; }

  .site-header[data-condensed] .nav-pill { padding: 9px 20px; font-size: var(--text-sm); }

  .grid--split,
  .grid--3 { grid-template-columns: minmax(0, 1fr); }

  .grid--12 { grid-template-columns: repeat(3, minmax(0, 1fr)); }

  .section { padding-block: var(--space-6); }
  .section--lg { padding-block: var(--section-y); }
  .band { padding-block: var(--space-6); }
}

@media (max-width: 640px) {
  .header-actions .status-chip { display: none; }

  .footer-deck { grid-template-columns: minmax(0, 1fr); }

  .grid--2,
  .grid--4 { grid-template-columns: minmax(0, 1fr); }

  .grid--12 { grid-template-columns: repeat(2, minmax(0, 1fr)); }

  .footer-list li { grid-template-columns: minmax(0, 1fr); }

  .masthead__brand { letter-spacing: 0.08em; }

  .chapter-index { font-size: var(--text-2xl); }
}

/* ==========================================================================
   动效降级
   ========================================================================== */
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }

  *,
  *::before,
  *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }

  .btn:hover,
  .nav-pill:hover { transform: none; }
}