:root {
  --bg: #f8fafc;
  --paper: #fffaf0;
  --surface: #ffffff;
  --ink: #172033;
  --muted: #5b6678;
  --line: #d8dee8;
  --primary: #1d4ed8;
  --accent: #a44912;
  --accent-2: #0f766e;
  --shadow: 0 20px 45px rgba(23, 32, 51, .08);
  --radius: 8px;
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background: var(--bg) url("../img/paper-texture.png");
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", "Microsoft YaHei", "Noto Sans CJK SC", sans-serif;
  line-height: 1.65;
}
img { max-width: 100%; height: auto; display: block; }
a { color: inherit; text-decoration: none; }
a:hover { color: var(--primary); }
a:focus-visible, button:focus-visible, input:focus-visible { outline: 3px solid rgba(29, 78, 216, .35); outline-offset: 3px; }
.skip-link { position: absolute; left: 16px; top: -60px; z-index: 20; background: var(--ink); color: #fff; padding: 10px 14px; border-radius: 6px; }
.skip-link:focus { top: 12px; }
.shell { width: min(1160px, calc(100% - 32px)); margin-inline: auto; }
.site-header { position: sticky; top: 0; z-index: 10; border-bottom: 1px solid rgba(216, 222, 232, .9); background: rgba(248, 250, 252, .94); backdrop-filter: blur(12px); }
.header-inner { min-height: 72px; display: flex; align-items: center; justify-content: space-between; gap: 20px; }
.brand { display: inline-flex; align-items: center; gap: 10px; font-weight: 800; min-height: 44px; }
.brand span { white-space: nowrap; }
.site-nav { display: flex; align-items: center; gap: 4px; }
.site-nav a { min-height: 44px; display: inline-flex; align-items: center; padding: 8px 12px; border-radius: 7px; color: var(--muted); font-weight: 650; }
.site-nav a:hover { background: #e8eef8; color: var(--ink); }
.nav-toggle { display: none; width: 44px; height: 44px; border: 1px solid var(--line); background: var(--surface); border-radius: 7px; cursor: pointer; }
.nav-toggle span { display: block; width: 20px; height: 2px; margin: 4px auto; background: var(--ink); }
.hero { min-height: calc(100dvh - 72px); display: grid; align-items: center; padding: 56px 0 36px; }
.hero-grid, .split, .two-col { display: grid; grid-template-columns: minmax(0, 1fr) minmax(320px, .86fr); gap: 48px; align-items: center; }
.hero-copy h1, .page-hero h1, .article-hero h1 { margin: 10px 0 16px; line-height: 1.08; letter-spacing: 0; font-size: clamp(2.5rem, 7vw, 5.8rem); }
.article-hero h1 small { display: block; margin-top: 8px; font-size: clamp(1.2rem, 2vw, 1.8rem); color: var(--muted); font-weight: 650; }
.hero-copy p, .page-hero p, .article-hero p { max-width: 760px; color: var(--muted); font-size: 1.12rem; }
.hero-media, .article-hero > img, .feature-card, .item-card, .glossary-card, .photo-panel { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); box-shadow: var(--shadow); }
.hero-media { padding: 18px; background: #111827 url("../img/metal-detail.jpg") center / cover; }
.photo-panel { width: 100%; aspect-ratio: 16 / 9; object-fit: cover; }
.hero-search, .page-search { margin-top: 24px; max-width: 620px; }
input[type="search"] { width: 100%; min-height: 52px; border: 1px solid #cbd5e1; border-radius: 7px; padding: 0 16px; font: inherit; background: #fff; color: var(--ink); }
.section { padding: 72px 0; }
.section.compact { padding: 38px 0; }
.band { background: #eef4f8; border-block: 1px solid var(--line); }
.section-heading { margin-bottom: 28px; max-width: 760px; }
.section-heading h2, .prose h2, .timeline-item h2 { margin: 6px 0 8px; line-height: 1.18; font-size: clamp(1.7rem, 3vw, 2.5rem); }
.section-heading p, .item-card p, .glossary-card p, .feature-card p { color: var(--muted); }
.eyebrow { color: var(--accent); font-size: .82rem; font-weight: 800; text-transform: uppercase; letter-spacing: .08em; }
.card-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 20px; }
.item-card { display: flex; min-height: 100%; flex-direction: column; padding: 16px; transition: transform .18s ease, box-shadow .18s ease, border-color .18s ease; }
.item-card:hover { transform: translateY(-3px); box-shadow: 0 24px 56px rgba(23, 32, 51, .12); border-color: #b9c6d8; color: var(--ink); }
.item-card img { width: 100%; aspect-ratio: 16 / 10; object-fit: contain; border-radius: 6px; background: #f2f5f9; margin-bottom: 16px; }
.item-card h3 { margin: 6px 0 6px; font-size: 1.35rem; line-height: 1.25; }
.text-link { display: inline-flex; min-height: 44px; align-items: center; color: var(--primary); font-weight: 800; }
.page-hero { padding: 72px 0 18px; }
.article { padding-bottom: 56px; }
.breadcrumb { display: flex; flex-wrap: wrap; gap: 8px; padding-top: 26px; color: var(--muted); font-size: .94rem; }
.breadcrumb a { color: var(--primary); }
.article-hero { padding: 34px 0 20px; }
.article-hero > img { padding: 18px; background: #f7f9fc; }
.fact-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 12px; padding: 14px 0 24px; }
.fact-grid div { border: 1px solid var(--line); background: var(--surface); border-radius: var(--radius); padding: 16px; }
.fact-grid span { display: block; color: var(--muted); font-size: .9rem; }
.fact-grid strong { display: block; margin-top: 4px; }
.prose { max-width: 780px; }
.prose p, .prose li { color: #2f3b4d; }
.check-list { display: grid; grid-template-columns: repeat(3, 1fr); gap: 12px; padding: 0; list-style: none; }
.check-list li { padding: 14px 16px; border: 1px solid var(--line); background: var(--surface); border-radius: var(--radius); }
.source-list { padding-left: 18px; }
.source-list a { color: var(--primary); text-decoration: underline; text-underline-offset: 3px; }
.notice { border-left: 4px solid var(--accent); background: #fff7ed; padding: 12px 14px; border-radius: 0 7px 7px 0; }
.timeline { position: relative; display: grid; gap: 18px; }
.timeline-item { position: relative; border-left: 4px solid var(--accent-2); background: var(--surface); border-radius: var(--radius); padding: 20px 24px; box-shadow: var(--shadow); }
.timeline-item span { color: var(--accent-2); font-weight: 800; }
.glossary-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 16px; }
.glossary-card { padding: 20px; }
.glossary-card h2 { margin: 0 0 8px; }
.feature-card { display: grid; grid-template-columns: .9fr 1fr; gap: 26px; align-items: center; padding: 18px; }
.site-footer { border-top: 1px solid var(--line); padding: 38px 0; background: #111827; color: #e5e7eb; }
.footer-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 26px; }
.site-footer p, .site-footer a { color: #cbd5e1; }
.sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0; }
[hidden] { display: none !important; }
@media (max-width: 900px) {
  .nav-toggle { display: block; }
  .site-nav { position: absolute; left: 16px; right: 16px; top: 72px; display: none; flex-direction: column; align-items: stretch; padding: 10px; border: 1px solid var(--line); border-radius: var(--radius); background: var(--surface); box-shadow: var(--shadow); }
  .site-nav.is-open { display: flex; }
  .site-nav a { width: 100%; }
  .hero-grid, .split, .two-col, .feature-card { grid-template-columns: 1fr; }
  .card-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .fact-grid, .footer-grid, .check-list { grid-template-columns: 1fr 1fr; }
}
@media (max-width: 640px) {
  .shell { width: min(100% - 24px, 1160px); }
  .hero { min-height: auto; padding-top: 36px; }
  .hero-copy h1, .page-hero h1, .article-hero h1 { font-size: 2.35rem; }
  .card-grid, .fact-grid, .footer-grid, .check-list, .glossary-grid { grid-template-columns: 1fr; }
  .section { padding: 48px 0; }
  .brand span { font-size: .95rem; }
}
@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { animation-duration: .01ms !important; animation-iteration-count: 1 !important; scroll-behavior: auto !important; transition-duration: .01ms !important; }
}