@import url("https://cdnjs.cloudflare.com/ajax/libs/font-awesome/6.5.0/css/all.min.css");

/* ─── Design tokens (ChatGPT design system) ─── */
:root {
  --color-surface-background: #fff;
  --color-surface-elevated: #f9f9f9;
  --color-surface-muted: #ececec;
  --color-surface-sidebar: #f9f9f9;
  --color-surface-composer: #fff;
  --color-text-primary: #0d0d0d;
  --color-text-secondary: #5d5d5d;
  --color-text-tertiary: #8f8f8f;
  --color-text-placeholder: #000000b3;
  --color-text-link: #2964aa;
  --color-border-light: #0d0d0d0d;
  --color-border-default: #0d0d0d1a;
  --color-border-medium: #00000026;
  --color-border-heavy: #0d0d0d26;
  --color-action-primary-bg: #000;
  --color-action-primary-fg: #fff;
  --color-action-primary-bg-hover: #0d0d0dcc;
  --color-action-secondary-bg: #ececec;
  --color-action-secondary-fg: #0d0d0d;
  --color-action-accent: #0169cc;
  --color-action-brand-purple: #ab68ff;
  --radius-sm: .25rem;
  --radius-md: .375rem;
  --radius-lg: .5rem;
  --radius-xl: .75rem;
  --radius-2xl: 1rem;
  --radius-3xl: 1.5rem;
  --radius-4xl: 2rem;
  --radius-pill: 9999px;
  --font-size-xs: 12px;
  --font-size-sm: 13px;
  --font-size-base: 14px;
  --font-size-md: 16px;
  --font-size-lg: 18px;
  --font-size-2xl: 24px;
  --font-weight-normal: 400;
  --font-weight-medium: 500;
  --font-weight-semibold: 600;
  --font-sans: "-apple-system-body", "ui-sans-serif", "-apple-system", "system-ui", "Segoe UI", "Helvetica", "Arial", sans-serif;
  --space-1: 4px; --space-2: 8px; --space-3: 12px; --space-4: 16px;
  --space-5: 20px; --space-6: 24px; --space-8: 32px; --space-10: 40px; --space-12: 48px;
}

/* ─── Reset ─── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html, body { overflow-x: hidden; max-width: 100%; }
body {
  font-family: var(--font-sans);
  font-size: var(--font-size-md);
  color: var(--color-text-primary);
  background: var(--color-surface-background);
  line-height: 1.6;
}
img { max-width: 100%; height: auto; display: block; }
a { color: inherit; text-decoration: none; }

/* ─── Top bar ─── */
.topbar {
  position: sticky; top: 0; z-index: 100;
  height: 56px;
  background: var(--color-surface-background);
  border-bottom: 1px solid var(--color-border-default);
  display: flex; align-items: center;
  padding: 0 var(--space-6);
}
.topbar-inner {
  display: flex; align-items: center; justify-content: space-between;
  width: 100%; max-width: 1200px; margin: 0 auto;
}
.logo-link { display: flex; align-items: center; gap: var(--space-2); text-decoration: none; }
.logo-svg { width: 28px; height: 28px; flex-shrink: 0; }
.logo-text { font-size: var(--font-size-lg); font-weight: var(--font-weight-semibold); color: var(--color-text-primary); }

.nav { display: flex; align-items: center; gap: var(--space-6); }
.nav-links { display: flex; align-items: center; gap: var(--space-4); list-style: none; }
.nav-links a {
  font-size: var(--font-size-base); color: var(--color-text-secondary);
  font-weight: var(--font-weight-medium); transition: color 0.15s;
}
.nav-links a:hover { color: var(--color-text-primary); }

.lang-switcher { display: flex; align-items: center; gap: 4px; font-size: var(--font-size-sm); }
.lang-switcher a { color: var(--color-text-secondary); padding: 2px 6px; border-radius: var(--radius-sm); }
.lang-switcher a:hover { color: var(--color-text-primary); background: var(--color-surface-muted); }
.lang-switcher a.active { color: var(--color-text-primary); font-weight: var(--font-weight-medium); }
.lang-sep { color: var(--color-text-tertiary); }

.nav-actions { display: flex; align-items: center; gap: var(--space-2); }

/* ─── Buttons ─── */
.btn {
  display: inline-flex; align-items: center; justify-content: center;
  border: none; cursor: pointer; font-family: var(--font-sans);
  font-size: var(--font-size-base); font-weight: var(--font-weight-medium);
  border-radius: var(--radius-pill); padding: 8px 16px; transition: all 0.15s;
  text-decoration: none; gap: var(--space-2);
}
.btn-primary {
  background: var(--color-action-primary-bg);
  color: var(--color-action-primary-fg);
}
.btn-primary:hover { background: var(--color-action-primary-bg-hover); }
.btn-secondary {
  background: transparent;
  color: var(--color-text-primary);
  border: 1px solid var(--color-border-heavy);
}
.btn-secondary:hover { background: var(--color-surface-muted); }
.btn-lg { padding: 12px 24px; font-size: var(--font-size-md); }
.btn-xl { padding: 14px 28px; font-size: var(--font-size-md); font-weight: var(--font-weight-semibold); }

/* ─── Mobile hamburger ─── */
.nav-toggle {
  display: none; background: none; border: 0;
  font-size: 24px; cursor: pointer; color: var(--color-text-primary);
  padding: var(--space-2); line-height: 1;
}

/* ─── Hero ─── */
.hero {
  min-height: calc(100vh - 56px);
  display: flex; flex-direction: column;
  align-items: center; justify-content: center;
  padding: var(--space-12) var(--space-6);
  text-align: center;
}
.hero-eyebrow {
  font-size: var(--font-size-sm); font-weight: var(--font-weight-medium);
  color: var(--color-text-secondary); letter-spacing: 0.05em; text-transform: uppercase;
  margin-bottom: var(--space-4);
}
.hero-title {
  font-size: clamp(2rem, 5vw, 3.5rem);
  font-weight: var(--font-weight-semibold);
  line-height: 1.15; max-width: 700px;
  margin-bottom: var(--space-6);
}
.hero-subtitle {
  font-size: var(--font-size-md); color: var(--color-text-secondary);
  max-width: 560px; margin-bottom: var(--space-8);
}
.hero-cta { display: flex; gap: var(--space-3); flex-wrap: wrap; justify-content: center; }

/* Composer box */
.composer-box {
  background: var(--color-surface-background);
  border: 1px solid var(--color-border-medium);
  border-radius: var(--radius-4xl);
  padding: 16px 20px;
  display: flex; align-items: center; gap: var(--space-3);
  max-width: 680px; width: 100%;
  margin-top: var(--space-8);
  box-shadow: 0 4px 80px 8px rgba(0,0,0,.04), 0 0 1px 0 rgba(0,0,0,.12);
  cursor: text;
}
.composer-box span {
  flex: 1; color: var(--color-text-placeholder); font-size: var(--font-size-md);
  text-align: left;
}
.composer-send {
  width: 32px; height: 32px; border-radius: 50%;
  background: var(--color-action-primary-bg);
  color: var(--color-action-primary-fg);
  display: flex; align-items: center; justify-content: center;
  font-size: 14px; cursor: pointer; flex-shrink: 0;
}

/* ─── Suggestions row ─── */
.suggestions {
  display: flex; gap: var(--space-2); flex-wrap: wrap;
  justify-content: center; margin-top: var(--space-4); max-width: 680px;
}
.suggestion-chip {
  background: var(--color-surface-elevated);
  border: 1px solid var(--color-border-default);
  border-radius: var(--radius-pill);
  padding: 6px 14px; font-size: var(--font-size-sm);
  color: var(--color-text-secondary); cursor: pointer;
  transition: background 0.15s; white-space: nowrap;
}
.suggestion-chip:hover { background: var(--color-surface-muted); }

/* ─── Section scaffold ─── */
.section { padding: 80px var(--space-6); }
.section-inner { max-width: 1100px; margin: 0 auto; }
.section-label {
  font-size: var(--font-size-xs); font-weight: var(--font-weight-semibold);
  text-transform: uppercase; letter-spacing: 0.1em;
  color: var(--color-text-tertiary); margin-bottom: var(--space-3);
}
.section-title {
  font-size: clamp(1.6rem, 3.5vw, 2.4rem);
  font-weight: var(--font-weight-semibold); line-height: 1.2;
  margin-bottom: var(--space-4);
}
.section-subtitle {
  font-size: var(--font-size-md); color: var(--color-text-secondary);
  max-width: 560px; margin-bottom: var(--space-10);
}
.section-bg { background: var(--color-surface-elevated); }

/* ─── Feature grid ─── */
.features-grid {
  display: grid; grid-template-columns: repeat(3, 1fr); gap: var(--space-6);
}
.feature-card {
  background: var(--color-surface-background);
  border: 1px solid var(--color-border-default);
  border-radius: var(--radius-2xl);
  padding: var(--space-6); transition: box-shadow 0.15s;
}
.feature-card:hover { box-shadow: 0 4px 16px rgba(0,0,0,.06); }
.feature-icon {
  width: 44px; height: 44px; border-radius: var(--radius-lg);
  background: var(--color-surface-muted);
  display: flex; align-items: center; justify-content: center;
  font-size: 20px; margin-bottom: var(--space-4);
}
.feature-title { font-size: var(--font-size-md); font-weight: var(--font-weight-semibold); margin-bottom: var(--space-2); }
.feature-desc { font-size: var(--font-size-sm); color: var(--color-text-secondary); line-height: 1.6; }

/* ─── Stats row ─── */
.stats-row { display: grid; grid-template-columns: repeat(4, 1fr); gap: var(--space-8); text-align: center; }
.stat-num { font-size: clamp(2rem, 4vw, 3rem); font-weight: var(--font-weight-semibold); line-height: 1; margin-bottom: var(--space-2); }
.stat-label { font-size: var(--font-size-sm); color: var(--color-text-secondary); }

/* ─── Use-case cards ─── */
.usecase-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: var(--space-6); }
.usecase-card {
  border: 1px solid var(--color-border-default);
  border-radius: var(--radius-2xl);
  overflow: hidden;
}
.usecase-img { width: 100%; height: 200px; object-fit: cover; }
.usecase-body { padding: var(--space-6); }
.usecase-tag {
  display: inline-block; font-size: var(--font-size-xs);
  font-weight: var(--font-weight-semibold); text-transform: uppercase;
  letter-spacing: 0.08em; color: var(--color-action-accent);
  margin-bottom: var(--space-3);
}
.usecase-title { font-size: var(--font-size-lg); font-weight: var(--font-weight-semibold); margin-bottom: var(--space-2); }
.usecase-desc { font-size: var(--font-size-sm); color: var(--color-text-secondary); }

/* ─── Split row ─── */
.split-row { display: grid; grid-template-columns: 1fr 1fr; gap: var(--space-12); align-items: center; }
.split-row.reverse { direction: rtl; }
.split-row.reverse > * { direction: ltr; }
.split-img { border-radius: var(--radius-2xl); width: 100%; aspect-ratio: 4/3; object-fit: cover; }
.split-body .section-title { margin-bottom: var(--space-3); }
.split-body .section-subtitle { margin-bottom: var(--space-6); }

/* ─── China keyword block ─── */
.keyword-cloud {
  display: flex; flex-wrap: wrap; gap: var(--space-2); margin: var(--space-6) 0;
}
.keyword-pill {
  background: var(--color-surface-muted);
  border-radius: var(--radius-pill); padding: 4px 12px;
  font-size: var(--font-size-sm); color: var(--color-text-secondary);
}

/* ─── Restrictions list ─── */
.restrictions-list { list-style: none; display: flex; flex-direction: column; gap: var(--space-3); }
.restrictions-list li {
  display: flex; align-items: flex-start; gap: var(--space-3);
  background: var(--color-surface-elevated); border-radius: var(--radius-xl);
  padding: var(--space-4) var(--space-5);
}
.restrictions-list li .icon { font-size: 18px; flex-shrink: 0; margin-top: 2px; }
.restrictions-list li strong { display: block; font-weight: var(--font-weight-medium); margin-bottom: 2px; }
.restrictions-list li span { font-size: var(--font-size-sm); color: var(--color-text-secondary); }

/* ─── FAQ ─── */
.faq-list { display: flex; flex-direction: column; gap: var(--space-2); }
.faq-item { border: 1px solid var(--color-border-default); border-radius: var(--radius-xl); overflow: hidden; }
.faq-q {
  width: 100%; background: none; border: 0; padding: var(--space-5) var(--space-6);
  display: flex; justify-content: space-between; align-items: center;
  font-family: var(--font-sans); font-size: var(--font-size-md);
  font-weight: var(--font-weight-medium); cursor: pointer; text-align: left;
  color: var(--color-text-primary);
}
.faq-q:hover { background: var(--color-surface-elevated); }
.faq-q .chevron { transition: transform 0.2s; font-size: 12px; color: var(--color-text-tertiary); }
.faq-item.open .faq-q .chevron { transform: rotate(180deg); }
.faq-a { display: none; padding: 0 var(--space-6) var(--space-5); font-size: var(--font-size-base); color: var(--color-text-secondary); }
.faq-item.open .faq-a { display: block; }

/* ─── CTA banner ─── */
.cta-banner {
  background: var(--color-text-primary); color: var(--color-action-primary-fg);
  border-radius: var(--radius-3xl); padding: 60px var(--space-10);
  text-align: center;
}
.cta-banner .section-title { color: #fff; }
.cta-banner .section-subtitle { color: rgba(255,255,255,.7); }
.cta-banner .btn-primary { background: #fff; color: #000; }
.cta-banner .btn-primary:hover { background: #f0f0f0; }

/* ─── Footer ─── */
.footer {
  background: var(--color-surface-elevated);
  border-top: 1px solid var(--color-border-default);
  padding: 48px var(--space-6) var(--space-8);
}
.footer-inner { max-width: 1100px; margin: 0 auto; }
.footer-grid { display: grid; grid-template-columns: 2fr 1fr 1fr 1fr; gap: var(--space-10); margin-bottom: var(--space-10); }
.footer-brand .logo-link { margin-bottom: var(--space-4); }
.footer-tagline { font-size: var(--font-size-sm); color: var(--color-text-secondary); max-width: 260px; }
.footer-col h4 { font-size: var(--font-size-sm); font-weight: var(--font-weight-semibold); margin-bottom: var(--space-4); }
.footer-col ul { list-style: none; display: flex; flex-direction: column; gap: var(--space-3); }
.footer-col ul a { font-size: var(--font-size-sm); color: var(--color-text-secondary); }
.footer-col ul a:hover { color: var(--color-text-primary); }
.footer-bottom {
  border-top: 1px solid var(--color-border-default);
  padding-top: var(--space-6);
  display: flex; justify-content: space-between; align-items: center;
  flex-wrap: wrap; gap: var(--space-4);
}
.footer-copy { font-size: var(--font-size-xs); color: var(--color-text-tertiary); }
.footer-links { display: flex; gap: var(--space-4); }
.footer-links a { font-size: var(--font-size-xs); color: var(--color-text-tertiary); }
.footer-links a:hover { color: var(--color-text-secondary); }

/* ─── Page header (inner pages) ─── */
.page-hero {
  padding: 80px var(--space-6) 60px;
  text-align: center;
  background: var(--color-surface-elevated);
  border-bottom: 1px solid var(--color-border-default);
}
.page-hero-title { font-size: clamp(1.8rem, 4vw, 3rem); font-weight: var(--font-weight-semibold); margin-bottom: var(--space-4); }
.page-hero-subtitle { font-size: var(--font-size-md); color: var(--color-text-secondary); max-width: 600px; margin: 0 auto; }

/* ─── Prose ─── */
.prose { max-width: 760px; margin: 0 auto; }
.prose h2 { font-size: 1.4rem; font-weight: var(--font-weight-semibold); margin: 2rem 0 .8rem; }
.prose h3 { font-size: 1.1rem; font-weight: var(--font-weight-semibold); margin: 1.5rem 0 .5rem; }
.prose p { font-size: var(--font-size-base); color: var(--color-text-secondary); margin-bottom: 1rem; line-height: 1.7; }
.prose ul { padding-left: 1.5rem; margin-bottom: 1rem; }
.prose ul li { font-size: var(--font-size-base); color: var(--color-text-secondary); margin-bottom: .4rem; line-height: 1.6; }

/* ─── Breadcrumb ─── */
.breadcrumb { font-size: var(--font-size-sm); color: var(--color-text-tertiary); margin-bottom: var(--space-6); }
.breadcrumb a { color: var(--color-text-tertiary); }
.breadcrumb a:hover { color: var(--color-text-secondary); }
.breadcrumb span { margin: 0 6px; }

/* ─── Image strip ─── */
.img-strip { display: grid; grid-template-columns: repeat(3, 1fr); gap: var(--space-4); margin: var(--space-10) 0; }
.img-strip img { border-radius: var(--radius-2xl); aspect-ratio: 4/3; width: 100%; object-fit: cover; }

/* ─── Responsive ─── */
@media (max-width: 768px) {
  .nav-links {
    display: none; position: fixed;
    inset: 56px 0 0 0; width: 100vw;
    flex-direction: column; align-items: center;
    background: var(--color-surface-background);
    padding: var(--space-6) 0; overflow-y: auto; z-index: 999;
    gap: var(--space-2); border-top: 1px solid var(--color-border-default);
  }
  .nav-links.open { display: flex; }
  .nav-links li { width: 100%; text-align: center; }
  .nav-links a { display: block; padding: 14px var(--space-6); font-size: var(--font-size-lg); }
  .lang-switcher { padding: var(--space-4) 0; gap: var(--space-4); }
  .lang-switcher .lang-sep { display: none; }
  .nav-toggle { display: block; }
  .nav-actions { display: none; }

  .hero { padding: 60px var(--space-4); min-height: auto; }
  .hero-cta { flex-direction: column; align-items: center; }
  .composer-box { margin-top: var(--space-6); }
  .suggestions { display: none; }

  .features-grid { grid-template-columns: 1fr; }
  .stats-row { grid-template-columns: repeat(2, 1fr); gap: var(--space-6); }
  .usecase-grid { grid-template-columns: 1fr; }
  .split-row { grid-template-columns: 1fr; }
  .split-row.reverse { direction: ltr; }
  .footer-grid { grid-template-columns: 1fr 1fr; gap: var(--space-6); }
  .img-strip { grid-template-columns: 1fr; }
  .section { padding: 60px var(--space-4); }
  .cta-banner { padding: 40px var(--space-5); }
}

@media (max-width: 480px) {
  .stats-row { grid-template-columns: 1fr 1fr; }
  .footer-grid { grid-template-columns: 1fr; }
}