:root {
  --bg: #0d1117;
  --surface: #161b22;
  --surface-2: #1f2630;
  --border: #30363d;
  --text: #e6edf3;
  --text-dim: #9da7b3;
  --accent: #3b82f6;
  --accent-hover: #60a5fa;
  --radius: 12px;
  --maxw: 880px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
    "Hiragino Sans GB", "Microsoft YaHei", Roboto, Helvetica, Arial, sans-serif;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--accent-hover); text-decoration: none; }
a:hover { text-decoration: underline; }

.container { max-width: var(--maxw); margin: 0 auto; padding: 0 24px; }

/* Header */
header {
  position: sticky; top: 0; z-index: 10;
  background: rgba(13, 17, 23, 0.85);
  backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--border);
}
.nav { display: flex; align-items: center; justify-content: space-between; height: 60px; }
.brand { display: flex; align-items: center; gap: 10px; font-weight: 700; font-size: 17px; color: var(--text); }
.brand img { width: 30px; height: 30px; border-radius: 7px; }
.nav-links { display: flex; align-items: center; gap: 22px; }
.nav-links a { color: var(--text-dim); font-size: 14px; }
.nav-links a:hover { color: var(--text); text-decoration: none; }
.lang-toggle {
  background: var(--surface-2); color: var(--text);
  border: 1px solid var(--border); border-radius: 8px;
  padding: 5px 12px; font-size: 13px; cursor: pointer;
}
.lang-toggle:hover { border-color: var(--accent); }

/* Hero */
.hero { padding: 80px 0 50px; text-align: center; }
.hero img.appicon { width: 96px; height: 96px; border-radius: 22px; box-shadow: 0 8px 30px rgba(0,0,0,.4); }
.hero h1 { font-size: 40px; margin: 24px 0 12px; letter-spacing: -0.02em; }
.hero .tagline { font-size: 19px; color: var(--text-dim); max-width: 640px; margin: 0 auto; }
.hero .cta { margin-top: 32px; display: flex; gap: 14px; justify-content: center; flex-wrap: wrap; }
.btn {
  display: inline-block; padding: 12px 24px; border-radius: 10px;
  font-weight: 600; font-size: 15px; border: 1px solid transparent; cursor: pointer;
}
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: var(--accent-hover); text-decoration: none; }
.btn-ghost { background: var(--surface); color: var(--text); border-color: var(--border); }
.btn-ghost:hover { border-color: var(--accent); text-decoration: none; }

/* Sections */
section { padding: 40px 0; border-top: 1px solid var(--border); }
h2 { font-size: 26px; margin: 0 0 8px; }
.lead { color: var(--text-dim); margin: 0 0 28px; }

.feature-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); gap: 16px; }
.card {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 22px;
}
.card h3 { margin: 0 0 8px; font-size: 17px; }
.card p { margin: 0; color: var(--text-dim); font-size: 14px; }

.flow { display: flex; flex-wrap: wrap; gap: 10px; align-items: center; margin: 8px 0 0; }
.flow .step {
  background: var(--surface-2); border: 1px solid var(--border);
  border-radius: 999px; padding: 8px 18px; font-size: 14px; font-weight: 600;
}
.flow .arrow { color: var(--accent); font-weight: 700; }

ul.faq { list-style: none; padding: 0; margin: 0; }
ul.faq > li { padding: 18px 0; border-bottom: 1px solid var(--border); }
ul.faq > li:last-child { border-bottom: none; }
ul.faq h3 { margin: 0 0 6px; font-size: 16px; }
ul.faq p { margin: 0; color: var(--text-dim); font-size: 14px; }

.contact-card {
  background: var(--surface); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 24px; margin-top: 8px;
}
.contact-card .row { display: flex; gap: 14px; align-items: baseline; padding: 8px 0; }
.contact-card .row .k { color: var(--text-dim); min-width: 110px; font-size: 14px; }

.privacy-body h3 { font-size: 17px; margin: 26px 0 6px; }
.privacy-body p, .privacy-body li { color: var(--text-dim); font-size: 15px; }
.privacy-body ul { padding-left: 20px; }

footer { border-top: 1px solid var(--border); padding: 28px 0; color: var(--text-dim); font-size: 13px; }

/* Language toggle: hide the non-active language to avoid flash.
   app.js sets <html lang> and toggles .lang-en/.lang-zh visibility. */
html[lang="en"] .lang-zh { display: none; }
html[lang="zh"] .lang-en { display: none; }

@media (max-width: 600px) {
  .hero h1 { font-size: 30px; }
  .hero .tagline { font-size: 16px; }
  .nav-links { gap: 14px; }
}