:root {
  --bg: #ffffff;
  --bg-alt: #f6f7f9;
  --text: #16181d;
  --muted: #5b6270;
  --line: #e4e7ec;
  --accent: #1f5eff;
  --accent-dark: #1749cc;
  --radius: 14px;
  --max: 1120px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Noto Sans CJK SC", "Helvetica Neue", Arial, sans-serif;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; scroll-padding-top: 72px; }
body { font-family: var(--font); color: var(--text); background: var(--bg); line-height: 1.7; -webkit-font-smoothing: antialiased; }
a { color: inherit; text-decoration: none; }
.container { width: 100%; max-width: var(--max); margin: 0 auto; padding: 0 24px; }

/* Language switching: show only the active language */
html[data-lang="zh"] [lang="en"] { display: none !important; }
html[data-lang="en"] [lang="zh-CN"] { display: none !important; }

/* Header */
.site-header { position: sticky; top: 0; z-index: 10; background: rgba(255,255,255,.88); backdrop-filter: saturate(180%) blur(12px); -webkit-backdrop-filter: saturate(180%) blur(12px); border-bottom: 1px solid var(--line); }
.header-inner { display: flex; align-items: center; justify-content: space-between; height: 64px; gap: 16px; }
.brand { font-weight: 700; font-size: 18px; letter-spacing: .02em; }
.brand-en { font-weight: 400; color: var(--muted); margin-left: 6px; }
.nav { display: flex; gap: 28px; }
.nav a { font-size: 15px; color: var(--muted); transition: color .2s; }
.nav a:hover, .nav a.active { color: var(--text); }
.header-actions { display: flex; align-items: center; gap: 10px; }
.lang-toggle { font: 600 13px var(--font); padding: 6px 14px; border: 1px solid var(--line); border-radius: 999px; background: #fff; cursor: pointer; transition: border-color .2s, color .2s; }
.lang-toggle:hover { border-color: var(--accent); color: var(--accent); }
.menu-toggle { display: none; width: 38px; height: 38px; border: 1px solid var(--line); border-radius: 10px; background: #fff; cursor: pointer; flex-direction: column; align-items: center; justify-content: center; gap: 4px; }
.menu-toggle span { display: block; width: 16px; height: 2px; background: var(--text); border-radius: 2px; }

/* Sections */
.section { padding: 96px 0; }
.section-alt { background: var(--bg-alt); }
.section-head { max-width: 680px; margin-bottom: 40px; }
h1 { font-size: clamp(32px, 5vw, 56px); line-height: 1.2; letter-spacing: -.01em; margin-bottom: 24px; }
h2 { font-size: clamp(26px, 3vw, 36px); line-height: 1.3; margin-bottom: 12px; }
h3 { font-size: 18px; line-height: 1.4; margin-bottom: 8px; }
.section-head p, .lead { color: var(--muted); font-size: 17px; }

/* Hero */
.hero { padding: 120px 0 104px; }
.eyebrow { color: var(--accent); font-weight: 600; font-size: 14px; letter-spacing: .06em; margin-bottom: 16px; }
.lead { max-width: 720px; font-size: 18px; }
.tags { list-style: none; display: flex; flex-wrap: wrap; gap: 8px; margin: 28px 0 36px; }
.tags li { font-size: 13px; padding: 4px 12px; border: 1px solid var(--line); border-radius: 999px; color: var(--muted); }
.hero-actions { display: flex; flex-wrap: wrap; gap: 12px; }

/* Buttons */
.btn { display: inline-flex; align-items: center; justify-content: center; padding: 12px 24px; border-radius: 999px; font-weight: 600; font-size: 15px; transition: background .2s, color .2s, border-color .2s; white-space: nowrap; }
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: var(--accent-dark); }
.btn-ghost { border: 1px solid var(--line); background: #fff; }
.btn-ghost:hover { border-color: var(--text); }

/* Cards */
.cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); gap: 20px; }
.cards-3 { grid-template-columns: repeat(3, 1fr); }
.card { background: #fff; border: 1px solid var(--line); border-radius: var(--radius); padding: 28px; transition: transform .2s, box-shadow .2s; }
.card:hover { transform: translateY(-2px); box-shadow: 0 10px 30px rgba(16,24,40,.06); }
.card p { color: var(--muted); font-size: 15px; }
.card-icon { font-weight: 700; font-size: 14px; color: var(--accent); margin-bottom: 16px; }
.card-placeholder { border-style: dashed; background: transparent; min-height: 180px; }
.card-placeholder:hover { transform: none; box-shadow: none; }
.badge { display: inline-block; font-size: 12px; padding: 2px 10px; border-radius: 999px; background: var(--bg-alt); color: var(--muted); margin-bottom: 16px; }

/* Knowledge */
.knowledge { display: flex; align-items: center; justify-content: space-between; gap: 32px; }
.knowledge p { color: var(--muted); font-size: 17px; max-width: 640px; }

/* Contact */
.contact { text-align: center; }
.contact p { color: var(--muted); margin-bottom: 20px; }
.contact-email { display: inline-block; font-size: clamp(20px, 3vw, 28px); font-weight: 600; color: var(--accent); border-bottom: 2px solid transparent; transition: border-color .2s; }
.contact-email:hover { border-color: var(--accent); }

/* Footer */
.site-footer { border-top: 1px solid var(--line); padding: 28px 0; font-size: 14px; }
.footer-inner { display: flex; justify-content: space-between; gap: 12px; flex-wrap: wrap; }
.muted { color: var(--muted); }

/* Responsive */
@media (max-width: 860px) {
  .cards-3 { grid-template-columns: 1fr; }
  .knowledge { flex-direction: column; align-items: flex-start; }
}
@media (max-width: 720px) {
  .menu-toggle { display: inline-flex; }
  .nav { position: absolute; top: 64px; left: 0; right: 0; flex-direction: column; gap: 0; background: #fff; border-bottom: 1px solid var(--line); display: none; }
  .nav.open { display: flex; }
  .nav a { padding: 14px 24px; border-top: 1px solid var(--line); }
  .section { padding: 72px 0; }
  .hero { padding: 80px 0 72px; }
}