/* =========================================================
   Alin Zhu — Personal Site
   Minimal · light & clean · (with optional dark mode)
   Edit the variables in :root to re-skin the whole site.
   ========================================================= */

:root {
  --bg: #ffffff;
  --surface: #f7f7f8;
  --text: #18181b;
  --muted: #71717a;
  --border: #e7e7ea;
  --accent: #4f46e5;
  --accent-soft: #eef2ff;
  --accent-contrast: #ffffff;
  --radius: 14px;
  --maxw: 940px;
  --shadow: 0 1px 2px rgba(0, 0, 0, .04), 0 12px 32px rgba(0, 0, 0, .05);
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, .05);
}

[data-theme="dark"] {
  --bg: #0b0b0f;
  --surface: #15151b;
  --text: #f4f4f5;
  --muted: #a1a1aa;
  --border: #27272a;
  --accent: #818cf8;
  --accent-soft: #1e1b3a;
  --accent-contrast: #0b0b0f;
  --shadow: 0 1px 2px rgba(0, 0, 0, .5), 0 12px 32px rgba(0, 0, 0, .5);
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, .5);
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  font-size: 17px;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  transition: background .3s ease, color .3s ease;
}

a { color: inherit; text-decoration: none; }

.container {
  width: 100%;
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 0 24px;
}

.accent { color: var(--accent); }

/* ---------------- Header / Nav ---------------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  background: color-mix(in srgb, var(--bg) 80%, transparent);
  backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--border);
}

.nav {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.brand {
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -.01em;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 28px;
}

.nav-links a {
  color: var(--muted);
  font-size: .95rem;
  font-weight: 500;
  transition: color .2s ease;
}

.nav-links a:hover { color: var(--text); }

.theme-toggle {
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  width: 38px;
  height: 38px;
  border-radius: 999px;
  cursor: pointer;
  font-size: 1rem;
  display: grid;
  place-items: center;
  white-space: nowrap;
  overflow: hidden;
  transition: border-color .2s ease, background .2s ease;
}
.theme-toggle:hover { border-color: var(--accent); }

.lang-toggle {
  border: 1px solid var(--border);
  background: var(--surface);
  color: var(--text);
  height: 38px;
  padding: 0 12px;
  border-radius: 999px;
  cursor: pointer;
  font-size: .82rem;
  font-weight: 600;
  letter-spacing: .02em;
  transition: border-color .2s ease, background .2s ease;
}
.lang-toggle:hover { border-color: var(--accent); }
.theme-toggle .icon-moon { display: none; }
[data-theme="dark"] .theme-toggle .icon-sun { display: none; }
[data-theme="dark"] .theme-toggle .icon-moon { display: inline; }

.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: 0;
  cursor: pointer;
  padding: 8px;
}
.nav-toggle span {
  width: 22px;
  height: 2px;
  background: var(--text);
  border-radius: 2px;
  transition: transform .25s ease, opacity .25s ease;
}
.nav-toggle[aria-expanded="true"] span:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] span:nth-child(2) { opacity: 0; }
.nav-toggle[aria-expanded="true"] span:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ---------------- Hero ---------------- */
.hero {
  padding: 96px 24px 72px;
  text-align: center;
}

.eyebrow {
  text-transform: uppercase;
  letter-spacing: .14em;
  font-size: .78rem;
  font-weight: 600;
  color: var(--accent);
  margin: 0 0 18px;
}

.hero h1 {
  font-size: clamp(2.1rem, 6vw, 3.4rem);
  line-height: 1.1;
  letter-spacing: -.02em;
  margin: 0 auto 20px;
  max-width: 16ch;
}

.lead {
  color: var(--muted);
  max-width: 60ch;
  margin: 0 auto;
  font-size: 1.08rem;
}

.hero-actions {
  display: flex;
  gap: 14px;
  justify-content: center;
  flex-wrap: wrap;
  margin: 32px 0 8px;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 12px 22px;
  border-radius: 999px;
  font-weight: 600;
  font-size: .95rem;
  cursor: pointer;
  border: 1px solid transparent;
  transition: transform .15s ease, background .2s ease, border-color .2s ease, color .2s ease;
}
.btn:active { transform: translateY(1px); }
.btn-primary {
  background: var(--accent);
  color: var(--accent-contrast);
}
.btn-primary:hover { filter: brightness(1.06); }
.btn-ghost {
  border-color: var(--border);
  color: var(--text);
  background: var(--surface);
}
.btn-ghost:hover { border-color: var(--accent); }

.stats {
  list-style: none;
  display: flex;
  justify-content: center;
  gap: 48px;
  flex-wrap: wrap;
  padding: 0;
  margin: 56px 0 0;
}
.stats li { display: flex; flex-direction: column; align-items: center; }
.stats strong { font-size: 1.8rem; font-weight: 700; letter-spacing: -.02em; }
.stats span { color: var(--muted); font-size: .85rem; }

/* ---------------- Sections ---------------- */
.section { padding: 72px 24px; }

.section-head { margin-bottom: 40px; }
.section-head h2 {
  font-size: clamp(1.6rem, 4vw, 2.2rem);
  letter-spacing: -.02em;
  margin: 0 0 8px;
}
.section-head p { color: var(--muted); margin: 0; }

/* ---------------- Work grid ---------------- */
.grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 24px;
}

/* When only one project card is present, center it and cap its width */
.grid > .card:only-child {
  grid-column: 1 / -1;
  max-width: 560px;
  margin-inline: auto;
}

.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  display: flex;
  flex-direction: column;
  transition: transform .2s ease, box-shadow .2s ease, border-color .2s ease;
}
.card:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow);
  border-color: color-mix(in srgb, var(--accent) 40%, var(--border));
}

.card-media {
  aspect-ratio: 16 / 9;
  width: 100%;
  display: block;
  object-fit: cover;
  background: var(--surface);
}
.card-media.grad-1 { background: linear-gradient(135deg, #6366f1, #a855f7); }
.card-media.grad-2 { background: linear-gradient(135deg, #0ea5e9, #22d3ee); }
.card-media.grad-3 { background: linear-gradient(135deg, #f59e0b, #ef4444); }
.card-media.grad-4 { background: linear-gradient(135deg, #10b981, #84cc16); }

.card-body { padding: 20px 22px 24px; display: flex; flex-direction: column; gap: 10px; }
.card-body h3 { margin: 0; font-size: 1.2rem; letter-spacing: -.01em; }
.card-body p { margin: 0; color: var(--muted); font-size: .96rem; }

.tags { list-style: none; display: flex; flex-wrap: wrap; gap: 8px; padding: 0; margin: 4px 0 0; }
.tags li {
  font-size: .76rem;
  font-weight: 500;
  color: var(--accent);
  background: var(--accent-soft);
  padding: 4px 10px;
  border-radius: 999px;
}

.card-links { display: flex; gap: 18px; margin-top: 6px; }
.card-links a { color: var(--text); font-weight: 600; font-size: .9rem; }
.card-links a:hover { color: var(--accent); }

/* ---------------- About ---------------- */
.about {
  display: grid;
  grid-template-columns: 1.6fr 1fr;
  gap: 48px;
  align-items: start;
}
.about-text p { margin: 0 0 18px; color: var(--text); }
.about-side {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
}
.about-side h3 { margin: 0 0 12px; font-size: 1rem; }
.about-side h3:not(:first-child) { margin-top: 26px; }
.about-side p { margin: 0; color: var(--muted); font-size: .95rem; }

/* ---------------- Contact ---------------- */
.social {
  list-style: none;
  display: flex;
  flex-wrap: wrap;
  gap: 22px;
  padding: 0;
  margin: 32px 0 0;
}
.social a { color: var(--muted); font-weight: 500; }
.social a:hover { color: var(--accent); }

/* ---------------- Footer ---------------- */
.site-footer {
  border-top: 1px solid var(--border);
  padding: 28px 0;
  margin-top: 24px;
}
.footer-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 12px;
  color: var(--muted);
  font-size: .9rem;
}
.footer-inner a:hover { color: var(--accent); }

/* ---------------- Prose / Policy page ---------------- */
.prose { max-width: 760px; margin: 0 auto; padding: 64px 24px 24px; }
.prose h1 { font-size: clamp(1.8rem, 4vw, 2.4rem); letter-spacing: -.02em; margin: 0 0 6px; }
.prose .last-updated { color: var(--muted); font-size: .9rem; margin: 0 0 36px; }
.prose h2 { font-size: 1.3rem; letter-spacing: -.01em; margin: 36px 0 12px; }
.prose p { color: var(--text); }
.prose ul { padding-left: 22px; }
.prose li { margin-bottom: 8px; color: var(--text); }
.prose strong { color: var(--text); }

/* ---------------- Support / Accessibility guide ---------------- */
.guide-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 22px 24px 24px;
  margin: 22px 0;
}
.guide-card h2 { font-size: 1.2rem; letter-spacing: -.01em; margin: 0 0 14px; }
.guide-card p { color: var(--text); margin: 0 0 12px; }
.guide-card p:last-child { margin-bottom: 0; }
.guide-card ul { padding-left: 22px; margin: 0; }
.guide-card li { margin-bottom: 10px; color: var(--text); }
.guide-card a { color: var(--accent); font-weight: 600; }

/* ---------------- Responsive ---------------- */
@media (max-width: 760px) {
  .nav-toggle { display: flex; }
  .nav-links {
    position: absolute;
    top: 64px;
    left: 0;
    right: 0;
    flex-direction: column;
    align-items: flex-start;
    gap: 4px;
    background: var(--bg);
    border-bottom: 1px solid var(--border);
    padding: 12px 24px 20px;
    transform: translateY(-12px);
    opacity: 0;
    pointer-events: none;
    transition: transform .2s ease, opacity .2s ease;
  }
  .nav-links.open { transform: translateY(0); opacity: 1; pointer-events: auto; }
  .nav-links a { padding: 8px 0; width: 100%; }

  .grid { grid-template-columns: 1fr; }
  .about { grid-template-columns: 1fr; gap: 28px; }
  .stats { gap: 32px; }
  .hero { padding: 72px 24px 56px; }
}

@media (prefers-reduced-motion: reduce) {
  * { scroll-behavior: auto !important; transition: none !important; }
}