/* vaichat.com — dark landing page */
:root {
  --bg: #0b0e16;
  --bg-alt: #10141f;
  --surface: #151a28;
  --border: #232b3e;
  --text: #e8ecf5;
  --muted: #9aa5bd;
  --accent: #7c5cff;
  --accent-2: #2dd4bf;
  --gradient: linear-gradient(120deg, #7c5cff, #2dd4bf);
  --radius: 14px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue",
    Arial, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font);
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}
img { max-width: 100%; height: auto; }
a { color: inherit; text-decoration: none; }
h1, h2, h3, h4 { line-height: 1.25; margin: 0 0 0.5em; }
p { margin: 0 0 1em; }

.container { max-width: 1120px; margin: 0 auto; padding: 0 24px; }
.container-narrow { max-width: 780px; }

/* ---- nav ---- */
.nav {
  position: sticky; top: 0; z-index: 50;
  background: rgba(11, 14, 22, 0.82);
  backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}
.nav-inner { display: flex; align-items: center; gap: 28px; height: 64px; }
.brand { display: flex; align-items: center; gap: 10px; font-weight: 700; font-size: 18px; }
.nav-links { display: flex; gap: 24px; margin-left: auto; }
.nav-links a { color: var(--muted); font-size: 15px; transition: color .15s; }
.nav-links a:hover { color: var(--text); }
.nav-actions { display: flex; align-items: center; gap: 12px; }
.nav-toggle { display: none; background: none; border: 0; color: var(--text); cursor: pointer; padding: 6px; }

/* language menu */
.lang-menu { position: relative; }
.lang-btn {
  display: flex; align-items: center; gap: 7px;
  background: transparent; border: 1px solid var(--border); border-radius: 999px;
  color: var(--muted); font: inherit; font-size: 14px; padding: 6px 14px; cursor: pointer;
  white-space: nowrap;
  transition: color .15s, border-color .15s;
}
.lang-btn:hover { color: var(--text); border-color: var(--muted); }
.lang-dropdown {
  position: absolute; right: 0; top: calc(100% + 8px);
  background: var(--surface); border: 1px solid var(--border); border-radius: 12px;
  padding: 6px; min-width: 160px; display: none; flex-direction: column;
  box-shadow: 0 12px 32px rgba(0, 0, 0, 0.45);
}
.lang-dropdown.open { display: flex; }
.lang-dropdown a { padding: 8px 12px; border-radius: 8px; font-size: 14px; color: var(--muted); }
.lang-dropdown a:hover { background: var(--bg-alt); color: var(--text); }
.lang-dropdown a.active { color: var(--accent-2); font-weight: 600; }

/* ---- buttons ---- */
.btn {
  display: inline-flex; align-items: center; gap: 9px; white-space: nowrap;
  border-radius: 999px; padding: 12px 24px;
  font-weight: 600; font-size: 15px; transition: transform .15s, box-shadow .15s, background .15s;
}
.btn-sm { padding: 8px 18px; font-size: 14px; }
.btn-primary {
  background: var(--gradient); color: #fff;
  box-shadow: 0 4px 20px rgba(124, 92, 255, 0.35);
}
.btn-primary:hover { transform: translateY(-1px); box-shadow: 0 6px 26px rgba(124, 92, 255, 0.5); }
.btn-ghost { border: 1px solid var(--border); color: var(--text); }
.btn-ghost:hover { border-color: var(--muted); }

/* ---- hero ---- */
.hero {
  position: relative; overflow: hidden;
  padding: 96px 0 72px;
}
.hero::before {
  content: ""; position: absolute; inset: -40% -20% auto;
  height: 130%; pointer-events: none;
  background:
    radial-gradient(600px 400px at 20% 10%, rgba(124, 92, 255, 0.22), transparent 65%),
    radial-gradient(600px 420px at 85% 25%, rgba(45, 212, 191, 0.14), transparent 65%);
}
.hero-inner { position: relative; display: grid; grid-template-columns: 1.05fr 1fr; gap: 48px; align-items: center; }
.badge {
  display: inline-block; margin-bottom: 18px;
  border: 1px solid var(--border); border-radius: 999px;
  padding: 5px 14px; font-size: 13px; color: var(--accent-2);
  background: rgba(45, 212, 191, 0.07);
}
.hero h1 { font-size: clamp(34px, 4.6vw, 54px); font-weight: 800; letter-spacing: -0.02em; }
.accent {
  background: var(--gradient);
  -webkit-background-clip: text; background-clip: text; color: transparent;
}
.lead { font-size: 19px; color: var(--muted); max-width: 34em; }
.hero-ctas { display: flex; flex-wrap: wrap; gap: 14px; margin: 26px 0 14px; }
.hero-note { font-size: 13.5px; color: var(--muted); opacity: 0.85; }
.hero-visual img {
  border-radius: var(--radius);
  border: 1px solid var(--border);
  box-shadow: 0 24px 64px rgba(0, 0, 0, 0.5);
}

/* ---- trust strip ---- */
.trust { border-block: 1px solid var(--border); background: var(--bg-alt); padding: 34px 0; }
.trust-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 32px; }
.trust-item h3 { font-size: 17px; margin-bottom: 4px; }
.trust-item p { color: var(--muted); font-size: 14.5px; margin: 0; }

/* ---- sections ---- */
.section { padding: 88px 0; }
.section-alt { background: var(--bg-alt); border-block: 1px solid var(--border); }
.section-title { font-size: clamp(26px, 3.2vw, 38px); font-weight: 800; letter-spacing: -0.01em; text-align: center; }
.section-sub { text-align: center; color: var(--muted); max-width: 44em; margin: 0 auto 12px; }

/* feature cards */
.cards { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; margin-top: 44px; }
.card {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 26px; transition: transform .18s, border-color .18s;
}
.card:hover { transform: translateY(-3px); border-color: #34405e; }
.card-icon {
  width: 44px; height: 44px; margin-bottom: 16px;
  display: grid; place-items: center; border-radius: 11px;
  background: rgba(124, 92, 255, 0.12); color: var(--accent);
}
.card-icon svg { width: 24px; height: 24px; }
.card h3 { font-size: 17.5px; }
.card p { color: var(--muted); font-size: 14.5px; margin: 0; }

/* platforms */
.platforms { display: grid; grid-template-columns: 1fr 1fr; gap: 24px; margin-top: 44px; }
.platform {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 32px;
}
.platform-head { display: flex; align-items: center; gap: 12px; margin-bottom: 12px; color: var(--accent-2); }
.platform-head h3 { margin: 0; font-size: 21px; color: var(--text); }
.platform > p { color: var(--muted); }
.checklist { list-style: none; margin: 18px 0 0; padding: 0; }
.checklist li {
  position: relative; padding: 6px 0 6px 30px; color: var(--text); font-size: 15px;
}
.checklist li::before {
  content: ""; position: absolute; left: 0; top: 10px;
  width: 18px; height: 18px; border-radius: 50%;
  background: rgba(45, 212, 191, 0.15);
  background-image: url('data:image/svg+xml;utf8,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" fill="none" stroke="%232dd4bf" stroke-width="3" stroke-linecap="round" stroke-linejoin="round"><path d="M5 13l4 4 10-10"/></svg>');
  background-size: 11px; background-position: center; background-repeat: no-repeat;
}

/* steps */
.steps {
  list-style: none; margin: 48px auto 0; padding: 0;
  display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px;
}
.step { display: flex; gap: 16px; }
.step-num {
  flex: none; width: 40px; height: 40px; border-radius: 50%;
  display: grid; place-items: center;
  background: var(--gradient); color: #fff; font-weight: 700; font-size: 17px;
}
.step h3 { font-size: 17px; margin-bottom: 4px; }
.step p { color: var(--muted); font-size: 14.5px; margin: 0; }

/* FAQ */
.faq { margin-top: 36px; display: flex; flex-direction: column; gap: 12px; }
.faq-item {
  background: var(--surface); border: 1px solid var(--border); border-radius: 12px;
  padding: 4px 22px;
}
.faq-item summary {
  cursor: pointer; font-weight: 600; padding: 15px 0; list-style: none;
  display: flex; justify-content: space-between; align-items: center; gap: 12px;
}
.faq-item summary::-webkit-details-marker { display: none; }
.faq-item summary::after {
  content: "+"; font-size: 22px; color: var(--muted); flex: none;
  transition: transform .2s;
}
.faq-item[open] summary::after { transform: rotate(45deg); }
.faq-item p { color: var(--muted); margin: 0 0 16px; font-size: 15px; }

/* CTA */
.cta { padding: 96px 0; text-align: center; position: relative; overflow: hidden; }
.cta::before {
  content: ""; position: absolute; inset: 0; pointer-events: none;
  background: radial-gradient(560px 300px at 50% 100%, rgba(124, 92, 255, 0.2), transparent 70%);
}
.cta-inner { position: relative; }
.cta h2 { font-size: clamp(26px, 3.4vw, 40px); font-weight: 800; }
.cta p { color: var(--muted); max-width: 40em; margin: 0 auto 8px; }
.cta-center { justify-content: center; }

/* footer */
.footer { border-top: 1px solid var(--border); background: var(--bg-alt); padding: 56px 0 0; }
.footer-inner {
  display: grid; grid-template-columns: 2fr 1fr 1fr; gap: 40px; padding-bottom: 40px;
}
.footer-brand p { color: var(--muted); font-size: 14.5px; margin-top: 12px; max-width: 30em; }
.footer-col h4 { font-size: 14px; text-transform: uppercase; letter-spacing: 0.06em; color: var(--muted); margin-bottom: 14px; }
.footer-col a { display: block; color: var(--muted); font-size: 14.5px; padding: 4px 0; }
.footer-col a:hover { color: var(--text); }
.footer-langs a.active { color: var(--accent-2); }
.footer-bottom {
  border-top: 1px solid var(--border); padding-block: 20px;
  color: var(--muted); font-size: 13.5px;
}
.footer-bottom p { margin: 0; }

/* ---- responsive ---- */
@media (max-width: 960px) {
  .hero-inner { grid-template-columns: 1fr; text-align: center; }
  .lead { margin-inline: auto; }
  .hero-ctas { justify-content: center; }
  .hero-visual { max-width: 640px; margin: 0 auto; }
  .cards { grid-template-columns: 1fr 1fr; }
  .steps { grid-template-columns: 1fr; max-width: 560px; }
  .trust-grid { grid-template-columns: 1fr; gap: 20px; text-align: center; }
  .platforms { grid-template-columns: 1fr; }
  .footer-inner { grid-template-columns: 1fr; gap: 28px; }
}
@media (max-width: 720px) {
  .nav-links {
    display: none; position: absolute; top: 64px; left: 0; right: 0;
    flex-direction: column; gap: 0; padding: 8px 24px 16px;
    background: var(--bg); border-bottom: 1px solid var(--border);
  }
  .nav-links.open { display: flex; }
  .nav-links a { padding: 12px 0; }
  .nav-toggle { display: block; }
  .cards { grid-template-columns: 1fr; }
  .hero { padding: 64px 0 48px; }
  .section { padding: 64px 0; }
}