:root {
  --bg: #f3f6fb;
  --surface: rgba(255, 255, 255, 0.88);
  --surface-strong: #ffffff;
  --surface-soft: #eef4ff;
  --text: #1a2433;
  --text-soft: #5c6b80;
  --primary: #3b82f6;
  --primary-strong: #2458c9;
  --accent: #14b8a6;
  --border: rgba(111, 141, 182, 0.2);
  --shadow: 0 18px 42px rgba(39, 76, 130, 0.12);
  --radius-xl: 28px;
  --radius-lg: 20px;
  --radius-md: 14px;
  --container: 1180px;
}

body[data-theme="dark"] {
  --bg: #0d1422;
  --surface: rgba(18, 28, 47, 0.86);
  --surface-strong: #121d31;
  --surface-soft: #17233b;
  --text: #edf3ff;
  --text-soft: #99abc9;
  --primary: #6ea8ff;
  --primary-strong: #8bb9ff;
  --accent: #2dd4bf;
  --border: rgba(125, 155, 205, 0.18);
  --shadow: 0 18px 42px rgba(0, 0, 0, 0.32);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  color: var(--text);
  background:
    radial-gradient(circle at top left, rgba(59, 130, 246, 0.15), transparent 34%),
    radial-gradient(circle at top right, rgba(20, 184, 166, 0.14), transparent 32%),
    linear-gradient(180deg, #f8fbff 0%, var(--bg) 100%);
  line-height: 1.7;
  transition: background 0.25s ease, color 0.25s ease;
}

body[data-theme="dark"] {
  background:
    radial-gradient(circle at top left, rgba(61, 138, 255, 0.18), transparent 30%),
    radial-gradient(circle at top right, rgba(45, 212, 191, 0.12), transparent 28%),
    linear-gradient(180deg, #0a1120 0%, var(--bg) 100%);
}

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

img {
  max-width: 100%;
}

button {
  font: inherit;
}

.container {
  width: min(calc(100% - 32px), var(--container));
  margin: 0 auto;
}

.reading-progress {
  position: fixed;
  inset: 0 0 auto;
  z-index: 999;
  height: 4px;
  background: rgba(127, 146, 179, 0.08);
}

.reading-progress span {
  display: block;
  width: 0;
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--accent));
  transition: width 0.08s linear;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  backdrop-filter: blur(18px);
  background: color-mix(in srgb, var(--bg) 78%, transparent);
  border-bottom: 1px solid rgba(127, 146, 179, 0.1);
}

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  min-height: 74px;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 14px;
}

.brand-mark {
  display: grid;
  place-items: center;
  width: 42px;
  height: 42px;
  border-radius: 14px;
  color: #fff;
  font-weight: 800;
  background: linear-gradient(135deg, var(--primary), var(--accent));
  box-shadow: var(--shadow);
}

.brand strong,
.brand small {
  display: block;
}

.brand small {
  color: var(--text-soft);
}

.topnav {
  display: inline-flex;
  align-items: center;
  gap: 20px;
  color: var(--text-soft);
  font-size: 0.95rem;
}

.topnav a:hover,
.topnav a:focus-visible {
  color: var(--primary);
}

.theme-toggle {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 14px;
  border: 1px solid var(--border);
  border-radius: 999px;
  color: var(--text);
  background: var(--surface);
  cursor: pointer;
}

.hero {
  padding: 72px 0 34px;
}

.hero-layout {
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(300px, 0.9fr);
  gap: 28px;
  align-items: stretch;
}

.hero-copy,
.hero-panel,
.toc-card,
.content-section,
.panel-card,
.stat-card,
.summary-card {
  background: var(--surface);
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
  backdrop-filter: blur(18px);
}

.hero-copy {
  border-radius: var(--radius-xl);
  padding: 42px;
}

.eyebrow,
.section-tag {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 6px 12px;
  border-radius: 999px;
  color: var(--primary);
  background: rgba(59, 130, 246, 0.12);
  font-weight: 700;
  letter-spacing: 0.02em;
}

.hero h1 {
  margin: 18px 0 18px;
  font-size: clamp(2.1rem, 4vw, 3.7rem);
  line-height: 1.18;
  letter-spacing: -0.03em;
}

.hero-summary {
  max-width: 64ch;
  color: var(--text-soft);
  font-size: 1.05rem;
}

.hero-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  margin: 28px 0 30px;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 12px 20px;
  border-radius: 999px;
  font-weight: 700;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.button:hover,
.button:focus-visible {
  transform: translateY(-1px);
}

.button--primary {
  color: #fff;
  background: linear-gradient(135deg, var(--primary), var(--accent));
  box-shadow: 0 12px 28px rgba(59, 130, 246, 0.24);
}

.button--ghost {
  border: 1px solid var(--border);
  background: var(--surface-soft);
}

.hero-meta {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
  padding: 0;
  margin: 0;
  list-style: none;
}

.hero-meta li {
  padding: 18px;
  border-radius: var(--radius-md);
  background: color-mix(in srgb, var(--surface-strong) 88%, transparent);
  border: 1px solid rgba(127, 146, 179, 0.14);
}

.hero-meta strong,
.hero-meta span {
  display: block;
}

.hero-meta strong {
  margin-bottom: 6px;
}

.hero-meta span {
  color: var(--text-soft);
  font-size: 0.95rem;
}

.hero-panel {
  display: grid;
  gap: 18px;
  align-self: stretch;
  border-radius: var(--radius-xl);
  padding: 24px;
}

.panel-card {
  border-radius: var(--radius-lg);
  padding: 28px;
}

.panel-card h2 {
  margin: 0 0 16px;
  font-size: 1.35rem;
}

.panel-points {
  margin: 0;
  padding-left: 20px;
  color: var(--text-soft);
}

.panel-points li + li {
  margin-top: 10px;
}

.stats-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
}

.stat-card {
  border-radius: var(--radius-lg);
  padding: 22px 20px;
}

.stat-card strong {
  display: block;
  margin-bottom: 10px;
  font-size: 1.7rem;
  color: var(--primary);
}

.article-shell {
  padding: 16px 0 88px;
}

.article-layout {
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
  gap: 24px;
  align-items: start;
}

.article-toc {
  position: sticky;
  top: 96px;
}

.toc-card {
  border-radius: var(--radius-lg);
  padding: 22px 20px;
}

.toc-title {
  margin: 0 0 16px;
  color: var(--text-soft);
  font-size: 0.92rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.toc-card nav {
  display: grid;
  gap: 10px;
}

.toc-card nav a {
  padding: 9px 12px;
  border-radius: 12px;
  color: var(--text-soft);
  transition: background 0.2s ease, color 0.2s ease;
}

.toc-card nav a:hover,
.toc-card nav a.is-active {
  color: var(--primary);
  background: rgba(59, 130, 246, 0.08);
}

.article-content {
  display: grid;
  gap: 24px;
}

.content-section {
  border-radius: var(--radius-xl);
  padding: 34px;
}

.content-section h2 {
  margin: 18px 0 16px;
  font-size: clamp(1.7rem, 3vw, 2.4rem);
  line-height: 1.25;
}

.content-section h3 {
  margin-top: 0;
}

.content-section p {
  margin: 0 0 14px;
  color: var(--text-soft);
}

.insight-grid,
.practice-grid,
.metric-cards {
  display: grid;
  gap: 16px;
  margin-top: 24px;
}

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

.insight-card,
.practice-card,
.metric-card,
.check-card,
.code-card {
  padding: 22px;
  border-radius: var(--radius-lg);
  background: color-mix(in srgb, var(--surface-strong) 94%, transparent);
  border: 1px solid rgba(127, 146, 179, 0.14);
}

.quote-block {
  margin: 26px 0 0;
  padding: 22px 24px;
  border-left: 4px solid var(--primary);
  border-radius: 0 var(--radius-lg) var(--radius-lg) 0;
  background: rgba(59, 130, 246, 0.07);
}

.quote-block p {
  margin: 0;
  color: var(--text);
  font-size: 1.06rem;
}

.layer-stack {
  display: grid;
  gap: 18px;
  margin-top: 24px;
}

.layer-card {
  padding: 24px 26px;
  border-radius: var(--radius-lg);
  border: 1px solid rgba(127, 146, 179, 0.14);
  background: linear-gradient(180deg, color-mix(in srgb, var(--surface-strong) 96%, transparent), color-mix(in srgb, var(--surface-soft) 72%, transparent));
}

.layer-card header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  margin-bottom: 10px;
}

.layer-card header span {
  padding: 6px 11px;
  border-radius: 999px;
  font-size: 0.88rem;
  font-weight: 700;
  color: var(--primary);
  background: rgba(59, 130, 246, 0.1);
}

.layer-card ul,
.compare-list ul,
.bullet-list {
  margin: 12px 0 0;
  padding-left: 20px;
  color: var(--text-soft);
}

.layer-card--unit {
  border-left: 6px solid #14b8a6;
}

.layer-card--api {
  border-left: 6px solid #4f46e5;
}

.layer-card--e2e {
  border-left: 6px solid #f97316;
}

.callout,
.metrics-banner {
  display: flex;
  gap: 10px;
  align-items: flex-start;
  margin-top: 24px;
  padding: 20px 22px;
  border-radius: var(--radius-lg);
  background: linear-gradient(135deg, rgba(59, 130, 246, 0.1), rgba(20, 184, 166, 0.08));
  border: 1px solid rgba(59, 130, 246, 0.12);
}

.timeline {
  display: grid;
  gap: 16px;
  margin-top: 24px;
}

.timeline-item {
  display: grid;
  grid-template-columns: 130px minmax(0, 1fr);
  gap: 18px;
  align-items: start;
}

.timeline-item__badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 12px 14px;
  border-radius: 999px;
  color: var(--primary);
  font-weight: 700;
  background: rgba(59, 130, 246, 0.08);
}

.timeline-item__content {
  padding: 20px 22px;
  border-radius: var(--radius-lg);
  background: color-mix(in srgb, var(--surface-strong) 95%, transparent);
  border: 1px solid rgba(127, 146, 179, 0.14);
}

.check-cards,
.practice-grid,
.metric-cards,
.double-panel,
.compare-list {
  grid-template-columns: repeat(2, minmax(0, 1fr));
}

.check-cards,
.double-panel,
.compare-list {
  display: grid;
  gap: 16px;
  margin-top: 24px;
}

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

.metrics-banner {
  margin-top: 20px;
}

.code-card pre {
  margin: 0;
  padding: 16px;
  overflow-x: auto;
  border-radius: 14px;
  color: #e5efff;
  background: #0e1727;
}

.code-card code {
  font-family: "Cascadia Code", "Consolas", monospace;
  font-size: 0.95rem;
}

.bullet-list li + li,
.checklist li + li {
  margin-top: 10px;
}

.compare-list > div {
  padding: 22px;
  border-radius: var(--radius-lg);
  border: 1px solid rgba(127, 146, 179, 0.14);
  background: color-mix(in srgb, var(--surface-strong) 94%, transparent);
}

.checklist {
  margin: 24px 0 0;
  padding-left: 0;
  list-style: none;
}

.checklist li {
  position: relative;
  padding: 16px 16px 16px 52px;
  border-radius: 16px;
  background: color-mix(in srgb, var(--surface-strong) 95%, transparent);
  border: 1px solid rgba(127, 146, 179, 0.14);
}

.checklist li::before {
  content: "✓";
  position: absolute;
  left: 18px;
  top: 15px;
  display: grid;
  place-items: center;
  width: 22px;
  height: 22px;
  border-radius: 50%;
  color: #fff;
  font-size: 0.9rem;
  background: linear-gradient(135deg, var(--primary), var(--accent));
}

.content-section--summary {
  position: relative;
  overflow: hidden;
}

.content-section--summary::after {
  content: "";
  position: absolute;
  inset: auto -70px -70px auto;
  width: 220px;
  height: 220px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(59, 130, 246, 0.18), transparent 68%);
  pointer-events: none;
}

.summary-card {
  margin-top: 22px;
  border-radius: var(--radius-lg);
  padding: 24px;
}

.summary-card h3 {
  margin-bottom: 8px;
}

.back-to-top {
  position: fixed;
  right: 24px;
  bottom: 24px;
  z-index: 80;
  width: 48px;
  height: 48px;
  border: 0;
  border-radius: 50%;
  color: #fff;
  background: linear-gradient(135deg, var(--primary), var(--accent));
  box-shadow: 0 14px 32px rgba(33, 107, 220, 0.28);
  cursor: pointer;
  opacity: 0;
  transform: translateY(8px);
  pointer-events: none;
  transition: opacity 0.2s ease, transform 0.2s ease;
}

.back-to-top.is-visible {
  opacity: 1;
  transform: translateY(0);
  pointer-events: auto;
}

.site-footer {
  border-top: 1px solid rgba(127, 146, 179, 0.12);
  padding: 24px 0 36px;
}

.footer-layout {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  color: var(--text-soft);
}

@media (max-width: 1080px) {
  .hero-layout,
  .article-layout,
  .timeline-item,
  .check-cards,
  .double-panel,
  .compare-list,
  .insight-grid,
  .practice-grid,
  .metric-cards,
  .hero-meta {
    grid-template-columns: 1fr;
  }

  .article-toc {
    position: static;
  }

  .timeline-item__badge {
    justify-content: flex-start;
  }
}

@media (max-width: 840px) {
  .topbar {
    flex-wrap: wrap;
    padding: 14px 0;
  }

  .topnav {
    width: 100%;
    order: 3;
    flex-wrap: wrap;
  }

  .hero {
    padding-top: 42px;
  }

  .hero-copy,
  .hero-panel,
  .content-section {
    padding: 24px;
  }
}

@media (max-width: 640px) {
  .container {
    width: min(calc(100% - 20px), var(--container));
  }

  .brand {
    width: 100%;
  }

  .theme-toggle {
    margin-left: auto;
  }

  .hero h1 {
    font-size: 2rem;
  }

  .hero-actions {
    flex-direction: column;
  }

  .button {
    width: 100%;
  }

  .content-section h2 {
    font-size: 1.6rem;
  }

  .footer-layout {
    flex-direction: column;
    align-items: flex-start;
  }
}