/* ============================================================
   Yongmei Zhang — personal site
   Clean, minimal, professional. Plain CSS, no build step.
   ============================================================ */

:root {
  --bg: #fbfaf8;
  --bg-alt: #f4f2ee;
  --text: #1c1f24;
  --muted: #5c6470;
  --faint: #8a919c;
  --accent: #0e7c6b;
  --accent-dark: #0a5f53;
  --border: #e6e1d8;
  --card-bg: #ffffff;
  --radius: 10px;
  --font-sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --font-serif: "Fraunces", Georgia, "Times New Roman", serif;
  --max-width: 1120px;
  --narrow: 760px;
}

* { box-sizing: border-box; margin: 0; padding: 0; }

html { scroll-behavior: smooth; }

body {
  font-family: var(--font-sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  font-size: 1.0625rem;
  -webkit-font-smoothing: antialiased;
}

.container {
  width: 100%;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 1.5rem;
}
.container.narrow { max-width: var(--narrow); }

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

/* ---------- Header ---------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(251, 250, 248, 0.92);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}
.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 68px;
}
.brand {
  font-family: var(--font-serif);
  font-weight: 600;
  font-size: 1.25rem;
  color: var(--text);
  letter-spacing: -0.01em;
}
.brand:hover { color: var(--text); }
.site-nav { display: flex; align-items: center; gap: 1.75rem; }
.site-nav a {
  color: var(--muted);
  font-size: 0.95rem;
  font-weight: 500;
}
.site-nav a:hover, .site-nav a.active { color: var(--text); }
.nav-cta {
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.45rem 1.1rem;
  color: var(--text) !important;
  background: var(--card-bg);
  transition: border-color 0.2s, background 0.2s;
}
.nav-cta:hover { border-color: var(--accent); background: #fff; }
.nav-toggle { display: none; }

/* ---------- Hero ---------- */
.hero { padding: 7rem 0 5.5rem; }
.hero-kicker {
  text-transform: uppercase;
  letter-spacing: 0.14em;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--faint);
  margin-bottom: 1.25rem;
}
.hero-name {
  font-family: var(--font-serif);
  font-weight: 500;
  font-size: clamp(2.6rem, 6vw, 4.25rem);
  line-height: 1.08;
  letter-spacing: -0.02em;
  margin-bottom: 1rem;
}
.hero-name .nickname { color: var(--muted); font-weight: 400; }
.hero-tagline {
  font-size: 1.35rem;
  font-weight: 600;
  color: var(--accent);
  letter-spacing: -0.01em;
  margin-bottom: 0.75rem;
}
.hero-role { color: var(--muted); margin-bottom: 1.5rem; }
.hero-role strong { color: var(--text); font-weight: 600; }
.hero-summary {
  max-width: 640px;
  color: var(--muted);
  font-size: 1.125rem;
  margin-bottom: 2.25rem;
}
.hero-actions { display: flex; gap: 0.9rem; flex-wrap: wrap; }

.btn {
  display: inline-block;
  font-weight: 600;
  font-size: 0.95rem;
  border-radius: 999px;
  padding: 0.8rem 1.6rem;
  transition: transform 0.15s ease, background 0.2s, border-color 0.2s;
}
.btn:active { transform: translateY(1px); }
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:hover { background: var(--accent-dark); color: #fff; }
.btn-ghost { border: 1px solid var(--border); color: var(--text); background: var(--card-bg); }
.btn-ghost:hover { border-color: var(--accent); color: var(--accent-dark); }

/* ---------- Sections ---------- */
.section { padding: 4.5rem 0; }
.section-alt { background: var(--bg-alt); border-top: 1px solid var(--border); border-bottom: 1px solid var(--border); }
.section-title {
  font-family: var(--font-serif);
  font-weight: 500;
  font-size: 1.9rem;
  letter-spacing: -0.015em;
  margin-bottom: 2rem;
}
.prose p { margin-bottom: 1.25rem; color: var(--muted); }
.prose p:last-child { margin-bottom: 0; }
.prose strong { color: var(--text); }
.text-link { font-weight: 600; }

/* ---------- Timeline ---------- */
.timeline { list-style: none; position: relative; padding-left: 1.75rem; }
.timeline::before {
  content: "";
  position: absolute;
  left: 6px;
  top: 8px;
  bottom: 8px;
  width: 2px;
  background: var(--border);
}
.timeline-item { position: relative; padding-bottom: 2.5rem; }
.timeline-item:last-child { padding-bottom: 0; }
.timeline-marker {
  position: absolute;
  left: -1.75rem;
  top: 7px;
  width: 14px;
  height: 14px;
  border-radius: 50%;
  background: var(--bg-alt);
  border: 2.5px solid var(--accent);
}
.timeline-period {
  font-size: 0.82rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--faint);
  margin-bottom: 0.35rem;
}
.timeline-body h3 { font-size: 1.15rem; font-weight: 600; letter-spacing: -0.01em; }
.timeline-org { color: var(--accent); font-weight: 600; font-size: 0.98rem; margin: 0.15rem 0 0.6rem; }
.timeline-desc { color: var(--muted); font-size: 1rem; max-width: 640px; }

/* ---------- Cards ---------- */
.cards { display: grid; grid-template-columns: repeat(2, 1fr); gap: 1.25rem; }
.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.6rem;
}
.card h3 { font-size: 1.05rem; font-weight: 600; margin-bottom: 0.25rem; letter-spacing: -0.01em; }
.card-org { color: var(--accent); font-weight: 600; font-size: 0.9rem; margin-bottom: 0.5rem; }
.card-desc { color: var(--muted); font-size: 0.95rem; }

/* ---------- Blog ---------- */
.page-hero { padding: 5rem 0 2rem; }
.page-title {
  font-family: var(--font-serif);
  font-weight: 500;
  font-size: clamp(2.2rem, 5vw, 3.2rem);
  letter-spacing: -0.02em;
  margin-bottom: 0.75rem;
}
.page-subtitle { color: var(--muted); font-size: 1.125rem; }

.post-teaser, .post-list-item {
  display: block;
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.5rem 1.6rem;
  margin: 1.5rem 0;
  transition: border-color 0.2s, transform 0.15s ease;
}
.post-teaser:hover, .post-list-item:hover { border-color: var(--accent); transform: translateY(-2px); }
.post-teaser-date, .post-list-date {
  display: block;
  font-size: 0.8rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--faint);
  margin-bottom: 0.4rem;
}
.post-teaser-title, .post-list-title {
  display: block;
  font-family: var(--font-serif);
  font-size: 1.4rem;
  font-weight: 500;
  color: var(--text);
  margin-bottom: 0.4rem;
}
.post-teaser-excerpt, .post-list-excerpt { display: block; color: var(--muted); font-size: 0.98rem; }

/* ---------- Post page ---------- */
.post { padding: 4rem 0 5rem; }
.post-meta { margin-bottom: 1.5rem; font-size: 0.95rem; font-weight: 500; }
.post-title {
  font-family: var(--font-serif);
  font-weight: 500;
  font-size: clamp(2rem, 4.5vw, 2.9rem);
  letter-spacing: -0.02em;
  line-height: 1.15;
  margin-bottom: 0.6rem;
}
.post-date { color: var(--faint); font-size: 0.95rem; margin-bottom: 2.5rem; }
.post .prose { font-size: 1.1rem; }

/* ---------- Contact ---------- */
.contact-block .prose { margin-bottom: 1.75rem; }

/* ---------- Footer ---------- */
.site-footer { border-top: 1px solid var(--border); padding: 2rem 0; }
.footer-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
  color: var(--faint);
  font-size: 0.9rem;
}

/* ---------- Reveal on scroll ---------- */
.reveal { opacity: 0; transform: translateY(14px); transition: opacity 0.6s ease, transform 0.6s ease; }
.reveal.visible { opacity: 1; transform: none; }
@media (prefers-reduced-motion: reduce) {
  .reveal { opacity: 1; transform: none; transition: none; }
  html { scroll-behavior: auto; }
}

/* ---------- Responsive ---------- */
@media (max-width: 720px) {
  .hero { padding: 4.5rem 0 4rem; }
  .cards { grid-template-columns: 1fr; }
  .nav-toggle {
    display: flex;
    flex-direction: column;
    justify-content: center;
    gap: 5px;
    background: none;
    border: none;
    cursor: pointer;
    padding: 0.5rem;
  }
  .nav-toggle span {
    display: block;
    width: 22px;
    height: 2px;
    background: var(--text);
    border-radius: 2px;
    transition: transform 0.2s, opacity 0.2s;
  }
  .site-nav {
    display: none;
    position: absolute;
    top: 68px;
    left: 0;
    right: 0;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    background: var(--bg);
    border-bottom: 1px solid var(--border);
    padding: 0.5rem 1.5rem 1rem;
  }
  .site-nav.open { display: flex; }
  .site-nav a { padding: 0.7rem 0; border-bottom: 1px solid var(--border); }
  .site-nav a:last-child { border-bottom: none; }
  .nav-cta { text-align: center; margin-top: 0.5rem; }
}