:root {
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --ink: #14213d;
  --text: #334155;
  --muted: #64748b;
  --surface: #ffffff;
  --soft: #f8fafc;
  --tint: #eff6ff;
  --border: #dbe4f0;
  --radius: 18px;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--text);
  background: var(--surface);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  font-size: 16px;
  line-height: 1.78;
  -webkit-font-smoothing: antialiased;
}
a { color: var(--primary); text-decoration-thickness: 1px; text-underline-offset: 3px; }
a:hover { color: var(--primary-dark); }
img { display: block; max-width: 100%; }
code { padding: 2px 6px; border-radius: 6px; background: #eaf1fb; font-size: .92em; }

.site-nav {
  position: sticky;
  top: 0;
  z-index: 20;
  border-bottom: 1px solid rgba(219, 228, 240, .9);
  background: rgba(255, 255, 255, .94);
  backdrop-filter: blur(12px);
}
.nav-inner {
  display: flex;
  max-width: 1120px;
  height: 60px;
  margin: 0 auto;
  padding: 0 24px;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}
.brand { color: var(--ink); font-size: 20px; font-weight: 800; text-decoration: none; }
.brand span { color: var(--primary); }
.nav-links { display: flex; gap: 22px; align-items: center; }
.nav-links a { color: var(--muted); font-size: 14px; text-decoration: none; }
.nav-links a:hover { color: var(--primary); }

.article-hero {
  overflow: hidden;
  border-bottom: 1px solid var(--border);
  background:
    radial-gradient(circle at 10% 0%, rgba(37, 99, 235, .14), transparent 31%),
    radial-gradient(circle at 90% 18%, rgba(14, 165, 233, .12), transparent 28%),
    linear-gradient(180deg, #fff 0%, #f8fbff 100%);
}
.hero-inner { max-width: 920px; margin: 0 auto; padding: 80px 24px 68px; }
.eyebrow {
  display: inline-flex;
  margin-bottom: 18px;
  padding: 6px 12px;
  border: 1px solid #bfdbfe;
  border-radius: 999px;
  color: #1d4ed8;
  background: rgba(239, 246, 255, .86);
  font-size: 13px;
  font-weight: 700;
}
h1, h2, h3 { color: var(--ink); line-height: 1.3; }
h1 { max-width: 850px; margin: 0 0 20px; font-size: clamp(36px, 6vw, 58px); letter-spacing: -.04em; }
.lead { max-width: 760px; margin: 0; color: #475569; font-size: 19px; }
.hero-actions { display: flex; gap: 12px; margin-top: 30px; flex-wrap: wrap; }
.button {
  display: inline-flex;
  min-height: 44px;
  padding: 10px 20px;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--primary);
  border-radius: 10px;
  background: var(--primary);
  color: #fff;
  font-weight: 700;
  text-decoration: none;
}
.button:hover { background: var(--primary-dark); color: #fff; }
.button-secondary { border-color: var(--border); background: #fff; color: var(--ink); }
.button-secondary:hover { border-color: #93c5fd; background: #f8fbff; color: var(--primary); }

.page-shell {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 240px;
  max-width: 1120px;
  margin: 0 auto;
  padding: 60px 24px 88px;
  gap: 64px;
  align-items: start;
}
.article { min-width: 0; }
.article section { margin-top: 56px; scroll-margin-top: 82px; }
.article section:first-child { margin-top: 0; }
.article h2 { margin: 0 0 18px; font-size: 30px; letter-spacing: -.02em; }
.article h3 { margin: 28px 0 10px; font-size: 20px; }
.article p { margin: 0 0 18px; }
.article ul, .article ol { margin: 0 0 20px; padding-left: 24px; }
.article li + li { margin-top: 8px; }
.answer-box, .boundary-box, .note-box {
  margin-bottom: 28px;
  padding: 24px 26px;
  border: 1px solid #bfdbfe;
  border-radius: var(--radius);
  background: var(--tint);
}
.answer-box strong { display: block; margin-bottom: 6px; color: #1e3a8a; font-size: 18px; }
.boundary-box { border-color: #fed7aa; background: #fff7ed; }
.boundary-box strong { color: #9a3412; }
.note-box { border-color: var(--border); background: var(--soft); }

.steps { display: grid; margin: 26px 0; gap: 16px; counter-reset: item; }
.step {
  display: grid;
  grid-template-columns: 42px 1fr;
  padding: 22px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: #fff;
  gap: 16px;
}
.step::before {
  display: inline-flex;
  width: 38px;
  height: 38px;
  align-items: center;
  justify-content: center;
  border-radius: 50%;
  background: var(--primary);
  color: #fff;
  content: counter(item);
  counter-increment: item;
  font-weight: 800;
}
.step h3 { margin: 4px 0 6px; font-size: 18px; }
.step p { margin: 0; color: var(--muted); }

.feature-grid, .link-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 18px; }
.info-card, .link-card {
  padding: 22px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: #fff;
}
.info-card h3, .link-card h3 { margin: 0 0 8px; font-size: 18px; }
.info-card p, .link-card p { margin: 0; color: var(--muted); font-size: 15px; }
.link-card { color: inherit; text-decoration: none; }
.link-card:hover { border-color: #93c5fd; background: #f8fbff; color: inherit; }
.link-card span { display: inline-block; margin-top: 14px; color: var(--primary); font-size: 14px; font-weight: 700; }

.product-shot {
  margin: 32px 0;
  padding: 18px;
  border: 1px solid var(--border);
  border-radius: 22px;
  background: #0f172a;
  box-shadow: 0 20px 50px rgba(15, 23, 42, .14);
}
.product-shot img { max-height: 620px; margin: 0 auto; border-radius: 12px; object-fit: contain; }
.product-shot figcaption { padding: 14px 4px 0; color: #cbd5e1; font-size: 14px; text-align: center; }

.comparison { width: 100%; margin: 28px 0; border-collapse: collapse; font-size: 15px; }
.comparison th, .comparison td { padding: 15px 16px; border: 1px solid var(--border); text-align: left; vertical-align: top; }
.comparison th { color: var(--ink); background: #f1f5f9; }
.comparison td:first-child { color: var(--ink); font-weight: 700; }

.toc { position: sticky; top: 88px; padding: 20px; border: 1px solid var(--border); border-radius: 14px; background: var(--soft); }
.toc strong { display: block; margin-bottom: 10px; color: var(--ink); font-size: 14px; }
.toc a { display: block; padding: 5px 0; color: var(--muted); font-size: 13px; text-decoration: none; }
.toc a:hover { color: var(--primary); }

.cta {
  margin-top: 60px;
  padding: 34px;
  border-radius: 22px;
  color: #dbeafe;
  background: #14213d;
}
.cta h2 { color: #fff; }
.cta p { max-width: 680px; color: #cbd5e1; }

.site-footer { border-top: 1px solid var(--border); background: var(--soft); }
.footer-inner { display: flex; max-width: 1120px; margin: 0 auto; padding: 34px 24px; justify-content: space-between; gap: 24px; color: var(--muted); font-size: 14px; }
.footer-links { display: flex; gap: 18px; flex-wrap: wrap; }
.footer-links a { color: var(--muted); }

@media (max-width: 820px) {
  .nav-links a:not(.nav-essential) { display: none; }
  .hero-inner { padding-top: 58px; }
  .page-shell { grid-template-columns: 1fr; gap: 0; }
  .toc { display: none; }
  .feature-grid, .link-grid { grid-template-columns: 1fr; }
  .comparison { display: block; overflow-x: auto; white-space: normal; }
  .footer-inner { flex-direction: column; }
}

@media (max-width: 520px) {
  .nav-inner, .hero-inner, .page-shell, .footer-inner { padding-left: 18px; padding-right: 18px; }
  h1 { font-size: 36px; }
  .lead { font-size: 17px; }
  .article h2 { font-size: 26px; }
  .answer-box, .boundary-box, .note-box, .cta { padding: 20px; }
  .step { grid-template-columns: 36px 1fr; padding: 18px; gap: 12px; }
  .step::before { width: 34px; height: 34px; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
}