:root {
  --color-surface: #fafafb;
  --color-surface-alt: #f0f0f1;
  --color-surface-deep: #e2e2e4;
  --color-ink: #353239;
  --color-ink-soft: #625d6a;
  --color-ink-muted: #7e7986;
  --color-line: #d7d6d8;
  --color-primary: #764ab5;
  --color-primary-ink: #ffffff;
  --color-primary-soft: #e8e1f1;
  --color-accent: #5c8217;
  --color-accent-ink: #ffffff;
  --color-highlight: #dee4d2;
  --color-focus: #557c0d;
  --color-contrast-surface: #131017;
  --color-contrast-ink: #e5e4e7;
  --color-contrast-line: #413f45;
  --color-contrast-accent: #99d926;
  --overlay-scrim: linear-gradient(180deg, rgba(19, 16, 23, 0.35) 0%, rgba(19, 16, 23, 0.72) 55%, rgba(19, 16, 23, 0.92) 100%);
  --font-heading: "Helvetica Neue", Arial, "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-body: "Helvetica Neue", Arial, "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-mono: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  --text-xs: 10.4px;
  --text-sm: 13.9px;
  --text-base: 16px;
  --text-lg: 21.3px;
  --text-xl: 28.4px;
  --text-2xl: 37.9px;
  --text-3xl: 50.5px;
  --text-4xl: 67.3px;
  --text-display: clamp(44px, 9.0vw, 115px);
  --text-figure: clamp(37px, 6.5vw, 83px);
  --weight-heading: 743;
  --weight-body: 400;
  --leading-body: 1.66;
  --leading-heading: 1.21;
  --tracking-heading: 0.003em;
  --radius-sm: 3px;
  --radius-md: 4px;
  --radius-lg: 5px;
  --radius-pill: 5px;
  --border-thin: 1px;
  --border-thick: 1px;
  --shadow-1: none;
  --shadow-2: none;
  --space-1: 8px;
  --space-2: 16px;
  --space-3: 24px;
  --space-4: 32px;
  --space-6: 48px;
  --space-8: 64px;
  --container: 1280px;
  --measure: 74ch;
  --gutter: 16px;
  --section-y: 81px;
  --section-y-lg: 113px;
}

/* ============ 1. 重置与中文排版 ============ */
*, *::before, *::after { box-sizing: border-box; }

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: 104px;
}

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);
  letter-spacing: 0.01em;
  word-break: break-word;
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4, h5, h6 {
  margin: 0;
  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); text-wrap: pretty; }
p:last-child { margin-bottom: 0; }

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

a { color: inherit; text-decoration: none; }

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

button { font: inherit; color: inherit; background: none; border: 0; cursor: pointer; }

table { border-collapse: collapse; width: 100%; }

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

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

.visually-hidden {
  position: absolute;
  width: 1px; height: 1px;
  margin: -1px; padding: 0;
  overflow: hidden;
  clip: rect(0 0 0 0);
  clip-path: inset(50%);
  white-space: nowrap;
  border: 0;
}

.skip-link {
  position: fixed;
  left: var(--space-2);
  top: -120px;
  z-index: 200;
  padding: 10px 18px;
  background-color: var(--color-primary);
  color: var(--color-primary-ink);
  border-radius: var(--radius-sm);
  font-size: var(--text-sm);
  font-weight: 600;
  transition: top 0.18s ease;
}
.skip-link:focus { top: var(--space-2); }

/* ============ 2. 布局工具 ============ */
.container {
  width: 100%;
  max-width: var(--container);
  margin-inline: auto;
  padding-inline: var(--space-3);
}

.grid-12 {
  display: grid;
  grid-template-columns: repeat(12, minmax(0, 1fr));
  gap: var(--gutter);
}

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

@media (min-width: 900px) {
  .split { grid-template-columns: minmax(0, 5fr) minmax(0, 7fr); }
  .split--4-8 { grid-template-columns: minmax(0, 4fr) minmax(0, 8fr); }
  .split--7-5 { grid-template-columns: minmax(0, 7fr) minmax(0, 5fr); }
}

.split__aside {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  padding: var(--space-4) var(--space-3);
  border-right: var(--border-thin) solid var(--color-contrast-line);
}

.split__main {
  background-color: var(--color-surface);
  padding: var(--space-4) var(--space-3);
}

.band { padding-block: var(--section-y); }
.band--lg { padding-block: var(--section-y-lg); }
.band--alt { background-color: var(--color-surface-alt); }
.band--deep {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}
.band--deep h1, .band--deep h2, .band--deep h3, .band--deep h4 { color: var(--color-contrast-ink); }
.band--deep a { color: var(--color-contrast-ink); }
.band--deep ::selection { background-color: var(--color-primary); color: var(--color-primary-ink); }

.prose { max-width: var(--measure); }
.prose p { margin-bottom: var(--space-3); }
.prose--sm p { font-size: var(--text-sm); color: var(--color-ink-soft); }
.band--deep .prose--sm p { color: color-mix(in srgb, var(--color-contrast-ink) 76%, transparent); }

/* ============ 3. 强调与数据字形 ============ */
.num, .figure {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-feature-settings: "tnum" 1;
}

.u-mark {
  padding-bottom: 2px;
  background-image: linear-gradient(var(--color-primary), var(--color-primary));
  background-repeat: no-repeat;
  background-size: 100% 2px;
  background-position: 0 100%;
}

.u-hl {
  background-color: var(--color-highlight);
  padding: 0 3px;
  border-radius: 2px;
}

.band--deep .u-mark {
  background-image: linear-gradient(var(--color-primary-soft), var(--color-primary-soft));
}

.chapter-no {
  display: block;
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-size: var(--text-4xl);
  line-height: 0.94;
  color: var(--color-primary);
}
.band--deep .chapter-no { color: var(--color-primary-soft); }

/* ============ 4. 按钮与标签 ============ */
.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-1);
  padding: 12px 20px;
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  background-color: var(--color-surface);
  color: var(--color-ink);
  font-size: var(--text-sm);
  font-weight: 600;
  letter-spacing: 0.03em;
  line-height: 1.2;
  transition: background-color 0.18s ease, color 0.18s ease, border-color 0.18s ease;
}

.btn:hover { background-color: var(--color-surface-alt); }

.btn--primary {
  background-color: var(--color-primary);
  border-color: var(--color-primary);
  color: var(--color-primary-ink);
}
.btn--primary:hover {
  background-color: color-mix(in srgb, var(--color-primary) 84%, #000);
  border-color: color-mix(in srgb, var(--color-primary) 84%, #000);
}

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

.btn--on-dark {
  background-color: transparent;
  border-color: var(--color-contrast-line);
  color: var(--color-contrast-ink);
}
.btn--on-dark:hover {
  background-color: var(--color-primary);
  border-color: var(--color-primary);
  color: var(--color-primary-ink);
}

.tag {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 3px 8px;
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  background-color: var(--color-surface);
  color: var(--color-ink-soft);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  line-height: 1.4;
}
.tag--accent {
  background-color: var(--color-accent);
  border-color: var(--color-accent);
  color: var(--color-accent-ink);
}
.tag--primary {
  background-color: var(--color-primary-soft);
  border-color: color-mix(in srgb, var(--color-primary) 32%, transparent);
  color: var(--color-primary);
}
.tag--ghost {
  background-color: transparent;
  border-color: var(--color-contrast-line);
  color: var(--color-contrast-ink);
}

/* ============ 5. 面包屑 ============ */
.crumbs {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-1);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  color: var(--color-ink-muted);
}
.crumbs li { display: flex; align-items: center; gap: var(--space-1); }
.crumbs li + li::before { content: "/"; color: var(--color-line); }
.crumbs a:hover { color: var(--color-primary); }
.band--deep .crumbs { color: color-mix(in srgb, var(--color-contrast-ink) 68%, transparent); }

/* ============ 6. 图片容器与数据浮层 ============ */
.media-frame {
  position: relative;
  overflow: hidden;
  isolation: isolate;
  border-radius: var(--radius-lg);
  background-color: var(--color-surface-deep);
}
.media-frame--deep { background-color: var(--color-contrast-surface); }
.media-frame--4x3 { aspect-ratio: 4 / 3; }
.media-frame--16x9 { aspect-ratio: 16 / 9; }
.media-frame--1x1 { aspect-ratio: 1 / 1; }
.media-frame--tall { aspect-ratio: 3 / 4; }

.media-frame__img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.media-frame__overlay {
  position: absolute;
  inset: 0;
  z-index: 1;
  background: var(--overlay-scrim);
  pointer-events: none;
}

.media-frame__caption {
  position: absolute;
  left: var(--space-2);
  right: var(--space-2);
  bottom: var(--space-2);
  z-index: 2;
  color: var(--color-contrast-ink);
  font-size: var(--text-xs);
  letter-spacing: 0.06em;
  line-height: 1.5;
}

.data-chip {
  position: absolute;
  z-index: 2;
  padding: 4px 8px;
  border: var(--border-thin) solid var(--color-contrast-line);
  border-radius: var(--radius-sm);
  background-color: color-mix(in srgb, var(--color-contrast-surface) 74%, transparent);
  color: var(--color-contrast-ink);
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-size: var(--text-xs);
  letter-spacing: 0.04em;
}
.data-chip--direction { color: var(--color-contrast-accent); }

/* ============ 7. 数据单元 ============ */
.stat { display: flex; flex-direction: column; gap: var(--space-1); }

.stat__value {
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-size: var(--text-figure);
  font-weight: var(--weight-heading);
  line-height: 0.94;
  color: var(--color-ink);
}
.band--deep .stat__value,
.split__aside .stat__value { color: var(--color-contrast-ink); }

.stat__label {
  font-size: var(--text-xs);
  letter-spacing: 0.14em;
  color: var(--color-ink-muted);
}
.band--deep .stat__label,
.split__aside .stat__label {
  color: color-mix(in srgb, var(--color-contrast-ink) 62%, transparent);
}

/* ============ 8. 章节目录与返回顶部 ============ */
.side-index {
  position: sticky;
  top: 104px;
  padding-left: var(--space-2);
  border-left: var(--border-thin) solid var(--color-line);
}
.band--deep .side-index { border-left-color: var(--color-contrast-line); }

.side-index__title {
  margin-bottom: var(--space-2);
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.18em;
  color: var(--color-ink-muted);
}
.band--deep .side-index__title {
  color: color-mix(in srgb, var(--color-contrast-ink) 60%, transparent);
}

.side-index__list { display: flex; flex-direction: column; gap: 2px; }

.side-index__link {
  position: relative;
  display: block;
  padding: 6px 10px 6px 0;
  font-size: var(--text-sm);
  line-height: 1.5;
  color: var(--color-ink-muted);
  transition: color 0.18s ease, background-color 0.18s ease;
}
.side-index__link:hover { color: var(--color-ink); }
.side-index__link.is-active {
  color: var(--color-primary);
  background-color: var(--color-primary-soft);
  padding-left: 8px;
}
.band--deep .side-index__link { color: color-mix(in srgb, var(--color-contrast-ink) 66%, transparent); }
.band--deep .side-index__link.is-active {
  color: var(--color-contrast-ink);
  background-color: color-mix(in srgb, var(--color-primary) 40%, transparent);
}

.back-to-top {
  position: fixed;
  left: var(--space-3);
  bottom: var(--space-3);
  z-index: 90;
  width: 46px;
  height: 46px;
  display: grid;
  place-items: center;
  border: var(--border-thin) solid var(--color-contrast-line);
  border-radius: var(--radius-sm);
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  opacity: 0;
  visibility: hidden;
  transform: translateY(8px);
  transition: opacity 0.2s ease, transform 0.2s ease, visibility 0.2s ease;
}
.back-to-top[data-visible="true"] { opacity: 1; visibility: visible; transform: none; }
.back-to-top:hover { border-color: var(--color-primary); color: var(--color-primary-soft); }

/* ============ 9. 页头 ============ */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background-color: var(--color-surface);
  border-bottom: var(--border-thin) solid var(--color-line);
  transition: background-color 0.2s ease;
}
.site-header[data-scrolled="true"] { background-color: var(--color-surface-alt); }

.site-header__inner {
  position: relative;
  max-width: var(--container);
  margin-inline: auto;
  display: grid;
  grid-template-columns: 1fr;
  align-items: stretch;
}

@media (min-width: 900px) {
  .site-header__inner { grid-template-columns: 3fr 9fr; }
}

.brand-block {
  position: relative;
  display: flex;
  align-items: center;
  padding: var(--space-2) var(--space-3) var(--space-2) var(--space-4);
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
}
.brand-block::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 5px;
  background-color: var(--color-primary);
}

.brand-block__link {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  min-width: 0;
}

.brand-block__mark {
  display: grid;
  place-items: center;
  flex: 0 0 auto;
  width: 36px;
  height: 36px;
  border-radius: var(--radius-sm);
  background-color: var(--color-primary);
  color: var(--color-primary-ink);
  font-family: var(--font-mono);
  font-variant-numeric: tabular-nums;
  font-size: var(--text-sm);
  font-weight: 700;
  letter-spacing: 0.02em;
}

.brand-block__text { display: flex; flex-direction: column; min-width: 0; }

.brand-block__name {
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: var(--text-lg);
  line-height: 1.15;
  color: var(--color-contrast-ink);
}

.brand-block__desc {
  margin-top: 2px;
  font-size: var(--text-xs);
  letter-spacing: 0.08em;
  color: color-mix(in srgb, var(--color-contrast-ink) 64%, transparent);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.site-nav {
  position: relative;
  display: flex;
  align-items: stretch;
  justify-content: space-between;
  gap: var(--space-2);
  padding-right: 10px;
  background-color: transparent;
}

.site-nav__list {
  display: flex;
  align-items: stretch;
  flex: 1 1 auto;
  min-width: 0;
}

.site-nav__item { display: flex; align-items: stretch; }

.site-nav__link {
  position: relative;
  display: flex;
  align-items: center;
  min-height: 74px;
  padding: 0 var(--space-2);
  color: var(--color-ink-soft);
  font-size: var(--text-base);
  letter-spacing: 0.02em;
  white-space: nowrap;
  transition: color 0.18s ease, background-color 0.18s ease;
}
.site-nav__link:hover {
  color: var(--color-ink);
  background-color: var(--color-primary-soft);
}
.site-nav__link::after {
  content: "";
  position: absolute;
  left: var(--space-2);
  right: var(--space-2);
  bottom: 0;
  height: 3px;
  background-color: transparent;
  transition: background-color 0.18s ease;
}
.site-nav__link[aria-current="page"] { color: var(--color-primary); }
.site-nav__link[aria-current="page"]::after { background-color: var(--color-primary); }

.nav-cta {
  display: inline-flex;
  align-items: center;
  align-self: center;
  padding: 10px 18px;
  border: var(--border-thin) solid var(--color-primary);
  border-radius: var(--radius-sm);
  color: var(--color-primary);
  font-size: var(--text-sm);
  font-weight: 600;
  letter-spacing: 0.04em;
  white-space: nowrap;
  transition: background-color 0.18s ease, color 0.18s ease;
}
.nav-cta:hover {
  background-color: var(--color-primary);
  color: var(--color-primary-ink);
}

.nav-current-band {
  position: absolute;
  right: 0;
  top: 0;
  bottom: 0;
  width: 8px;
  background-color: var(--color-surface-deep);
  transition: background-color 0.2s ease;
}
.nav-current-band[data-active="true"] { background-color: var(--color-primary); }

.nav-toggle {
  display: none;
  align-items: center;
  gap: var(--space-1);
  align-self: center;
  padding: 12px 14px;
  border: var(--border-thin) solid var(--color-line);
  border-radius: var(--radius-sm);
  color: var(--color-ink);
  font-size: var(--text-sm);
  letter-spacing: 0.06em;
}

.nav-toggle__bars {
  position: relative;
  display: block;
  width: 16px;
  height: 10px;
}
.nav-toggle__bars::before,
.nav-toggle__bars::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  height: 1px;
  background-color: currentColor;
  transition: transform 0.2s ease;
}
.nav-toggle__bars::before { top: 0; }
.nav-toggle__bars::after { bottom: 0; }
.nav-toggle[aria-expanded="true"] .nav-toggle__bars::before { transform: translateY(4px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] .nav-toggle__bars::after { transform: translateY(-5px) rotate(-45deg); }

@media (max-width: 899px) {
  .site-header__inner { grid-template-columns: 1fr; }
  .nav-toggle { display: inline-flex; order: 2; }
  .site-nav {
    padding: var(--space-2) var(--space-3);
    border-top: var(--border-thin) solid var(--color-line);
    align-items: center;
  }
  .site-nav__list {
    position: absolute;
    left: 0;
    right: 0;
    top: 100%;
    display: none;
    flex-direction: column;
    align-items: stretch;
    background-color: var(--color-surface);
    border-top: var(--border-thin) solid var(--color-line);
    border-bottom: var(--border-thin) solid var(--color-line);
  }
  .site-nav[data-open="true"] .site-nav__list { display: flex; }
  .site-nav__item { display: block; }
  .site-nav__link {
    min-height: 0;
    padding: var(--space-2) var(--space-3);
    border-bottom: var(--border-thin) solid var(--color-line);
  }
  .site-nav__link::after {
    left: 0;
    right: auto;
    top: 0;
    bottom: 0;
    width: 3px;
    height: auto;
  }
  .nav-cta { margin-left: auto; }
}

/* ============ 10. 页脚 ============ */
.site-footer {
  background-color: var(--color-contrast-surface);
  color: var(--color-contrast-ink);
  border-top: var(--border-thin) solid var(--color-contrast-line);
}

.site-footer__wordmark {
  max-width: var(--container);
  margin: 0 auto;
  padding: var(--space-6) var(--space-3) var(--space-3);
  border-bottom: var(--border-thin) solid var(--color-contrast-line);
  font-family: var(--font-heading);
  font-weight: var(--weight-heading);
  font-size: clamp(var(--text-3xl), 9vw, var(--text-4xl));
  line-height: 0.92;
  letter-spacing: -0.02em;
  color: var(--color-contrast-ink);
  white-space: nowrap;
  overflow: hidden;
}

.footer-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: var(--space-6);
  padding-block: var(--space-6);
}

@media (min-width: 760px) {
  .footer-grid { grid-template-columns: minmax(0, 3fr) minmax(0, 4fr) minmax(0, 4fr); gap: var(--space-4); }
}

.footer-col { min-width: 0; }

.footer-col__title {
  margin-bottom: var(--space-2);
  font-family: var(--font-body);
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.18em;
  color: color-mix(in srgb, var(--color-contrast-ink) 58%, transparent);
}

.footer-links { display: flex; flex-direction: column; gap: 8px; }

.footer-links a {
  display: inline-block;
  padding-bottom: 2px;
  border-bottom: var(--border-thin) solid transparent;
  font-size: var(--text-sm);
  color: var(--color-contrast-ink);
  transition: color 0.18s ease, border-color 0.18s ease;
}
.footer-links a:hover {
  color: var(--color-primary-soft);
  border-bottom-color: var(--color-primary-soft);
}

.footer-note {
  max-width: 46ch;
  margin-bottom: var(--space-2);
  font-size: var(--text-sm);
  line-height: 1.7;
  color: color-mix(in srgb, var(--color-contrast-ink) 78%, transparent);
}

.footer-contact {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-bottom: var(--space-3);
}

.footer-contact li {
  display: grid;
  grid-template-columns: 48px minmax(0, 1fr);
  gap: var(--space-2);
  font-size: var(--text-sm);
}

.footer-contact__key {
  padding-top: 3px;
  font-family: var(--font-mono);
  font-size: var(--text-xs);
  letter-spacing: 0.1em;
  color: color-mix(in srgb, var(--color-contrast-ink) 54%, transparent);
}

.footer-contact__val { color: var(--color-contrast-ink); word-break: break-word; }

.footer-cta { margin-top: var(--space-1); }

.footer-bottom {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-2);
  padding-block: var(--space-3);
  border-top: var(--border-thin) solid var(--color-contrast-line);
  font-size: var(--text-xs);
  letter-spacing: 0.05em;
  color: color-mix(in srgb, var(--color-contrast-ink) 64%, transparent);
}

.footer-legal { margin: 0; }

.footer-legal-links { display: flex; flex-wrap: wrap; gap: var(--space-3); }
.footer-legal-links a {
  border-bottom: var(--border-thin) solid transparent;
  transition: color 0.18s ease, border-color 0.18s ease;
}
.footer-legal-links a:hover {
  color: var(--color-contrast-ink);
  border-bottom-color: var(--color-primary-soft);
}

/* ============ 11. 动效偏好 ============ */
@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;
  }
  .back-to-top { transform: none; }
}