/* ============================================================
   main.css — Zhengfa DANG personal homepage
   Design: Editorial Monochrome / Linear-inspired
   ============================================================ */

/* ── Custom Properties ─────────────────────────────────────── */
:root {
  --bg:          #fafafa;
  --bg-alt:      #f4f4f5;
  --bg-card:     #ffffff;
  --border:      #e4e4e7;
  --border-hover:#a1a1aa;
  --text:        #0a0a0a;
  --text-muted:  #71717a;
  --text-subtle: #a1a1aa;
  --accent:      #3b82f6;
  --accent-dim:  #dbeafe;
  --accent-hover:#2563eb;
  --mono:        'JetBrains Mono', 'SF Mono', 'Fira Code', monospace;
  --sans:        'Inter', system-ui, -apple-system, sans-serif;
  --radius:      10px;
  --radius-lg:   16px;
  --shadow-sm:   0 1px 3px rgba(0,0,0,.06), 0 1px 2px rgba(0,0,0,.04);
  --shadow-md:   0 4px 12px rgba(0,0,0,.08), 0 2px 4px rgba(0,0,0,.04);
  --transition:  200ms cubic-bezier(.4,0,.2,1);
  --container:   1040px;
  --nav-h:       80px;
  --nav-h-min:   56px;
}

/* ── Reset & Base ──────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

html {
  scroll-behavior: smooth;
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: var(--sans);
  font-size: 1rem;
  line-height: 1.7;
  color: var(--text);
  background: var(--bg);
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

img { max-width: 100%; height: auto; display: block; }
a { color: var(--accent); text-decoration: none; transition: color var(--transition); }
a:hover { color: var(--accent-hover); }
ul { list-style: none; }

/* ── Typography ────────────────────────────────────────────── */
h1, h2, h3, h4 {
  font-weight: 700;
  line-height: 1.2;
  letter-spacing: -0.02em;
  color: var(--text);
}

h1 { font-size: clamp(2.25rem, 5vw, 3.5rem); }
h2 { font-size: clamp(1.5rem, 3vw, 2rem); }
h3 { font-size: 1.125rem; font-weight: 600; }

.mono {
  font-family: var(--mono);
  font-size: 0.8125rem;
  letter-spacing: 0.02em;
}

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

section {
  padding: 96px 0;
}

@media (max-width: 768px) {
  section { padding: 64px 0; }
}

/* ── Section Header ────────────────────────────────────────── */
.section-header {
  margin-bottom: 56px;
}

.section-label {
  font-family: var(--mono);
  font-size: 0.75rem;
  font-weight: 500;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent);
  display: block;
  margin-bottom: 8px;
}

.section-title {
  font-size: clamp(1.5rem, 3vw, 2rem);
  color: var(--text);
  margin-bottom: 12px;
}

.section-sub {
  color: var(--text-muted);
  font-size: 1rem;
  max-width: 560px;
}

/* ── Navigation ────────────────────────────────────────────── */
.nav {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  height: var(--nav-h);
  background: rgba(250,250,250,.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid transparent;
  transition: height 280ms cubic-bezier(.4,0,.2,1), background var(--transition), border-color var(--transition), box-shadow var(--transition);
}
.nav.is-scrolled {
  height: var(--nav-h-min);
  border-bottom-color: var(--border);
  box-shadow: 0 1px 0 rgba(0,0,0,0.02);
}
.nav > .container { height: 100%; }

.nav-inner {
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}

.nav-brand {
  font-weight: 700;
  font-size: 0.9375rem;
  color: var(--text);
  letter-spacing: -0.01em;
  white-space: nowrap;
}
.nav-brand:hover { color: var(--text); }

.nav-links {
  display: flex;
  align-items: center;
  gap: 4px;
}

.nav-links a {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--text-muted);
  padding: 6px 12px;
  border-radius: 6px;
  transition: color var(--transition), background var(--transition);
}

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

.nav-actions {
  display: flex;
  align-items: center;
  gap: 8px;
}

/* Mobile nav toggle */
.nav-hamburger {
  display: none;
  background: none;
  border: 1px solid var(--border);
  border-radius: 6px;
  width: 36px;
  height: 36px;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  color: var(--text);
  flex-direction: column;
  gap: 4px;
  padding: 8px;
}
.nav-hamburger span {
  display: block;
  width: 100%;
  height: 1.5px;
  background: currentColor;
  transition: transform var(--transition), opacity var(--transition);
}

@media (max-width: 640px) {
  .nav-links { display: none; }
  .nav-hamburger { display: flex; }

  .nav-links.is-open {
    display: flex;
    flex-direction: column;
    align-items: flex-start;
    gap: 2px;
    position: absolute;
    top: var(--nav-h);
    left: 0;
    right: 0;
    background: var(--bg);
    border-bottom: 1px solid var(--border);
    padding: 12px 24px 20px;
  }

  .nav-links.is-open a {
    width: 100%;
    padding: 10px 12px;
    font-size: 1rem;
  }
}

/* ── Hero ──────────────────────────────────────────────────── */
#hero {
  padding-top: calc(var(--nav-h) + 64px);
  padding-bottom: 96px;
  min-height: 100svh;
  display: flex;
  align-items: center;
}

.hero-inner {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 64px;
  align-items: center;
}

.hero-content {
  max-width: 600px;
}

.hero-eyebrow {
  display: flex;
  align-items: center;
  gap: 8px;
  margin-bottom: 24px;
}

.hero-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: var(--accent);
  animation: pulse-dot 2.5s ease-in-out infinite;
}

@keyframes pulse-dot {
  0%, 100% { opacity: 1; transform: scale(1); }
  50%       { opacity: .5; transform: scale(.8); }
}

.hero-eyebrow-text {
  font-family: var(--mono);
  font-size: 0.8125rem;
  color: var(--text-muted);
  letter-spacing: 0.04em;
}

.hero-name {
  font-size: clamp(2.5rem, 6vw, 4rem);
  letter-spacing: -0.03em;
  line-height: 1.05;
  margin-bottom: 8px;
}

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

.hero-tagline {
  font-size: 1.0625rem;
  color: var(--text-muted);
  font-weight: 400;
  margin-bottom: 24px;
  letter-spacing: -0.01em;
}

.hero-bio {
  font-size: 1rem;
  color: var(--text-muted);
  line-height: 1.75;
  margin-bottom: 40px;
  max-width: 520px;
}

.hero-ctas {
  display: flex;
  gap: 12px;
  flex-wrap: wrap;
}

/* Buttons */
.btn-primary {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  font-size: 0.9375rem;
  font-weight: 600;
  color: #fff;
  background: var(--accent);
  border: 1px solid var(--accent);
  border-radius: 8px;
  transition: background var(--transition), transform var(--transition), box-shadow var(--transition);
  cursor: pointer;
  white-space: nowrap;
}
.btn-primary:hover {
  color: #fff;
  background: var(--accent-hover);
  border-color: var(--accent-hover);
  transform: translateY(-1px);
  box-shadow: var(--shadow-md);
}

.btn-secondary {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 20px;
  font-size: 0.9375rem;
  font-weight: 600;
  color: var(--text);
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 8px;
  transition: border-color var(--transition), transform var(--transition), box-shadow var(--transition);
  cursor: pointer;
  white-space: nowrap;
}
.btn-secondary:hover {
  color: var(--text);
  border-color: var(--border-hover);
  transform: translateY(-1px);
  box-shadow: var(--shadow-sm);
}

.btn-primary svg, .btn-secondary svg { width: 16px; height: 16px; flex-shrink: 0; }

/* Portrait */
.hero-portrait-wrap {
  position: relative;
  flex-shrink: 0;
}

.hero-portrait {
  width: 200px;
  height: 200px;
  border-radius: var(--radius-lg);
  object-fit: cover;
  border: 1px solid var(--border);
  box-shadow: var(--shadow-md);
  transition: box-shadow var(--transition);
}

.hero-portrait-wrap::before {
  content: '';
  position: absolute;
  inset: -6px;
  border-radius: calc(var(--radius-lg) + 6px);
  border: 1px solid var(--border);
  pointer-events: none;
}

@media (max-width: 768px) {
  .hero-inner {
    grid-template-columns: 1fr;
    gap: 40px;
  }
  .hero-portrait-wrap { order: -1; }
  .hero-portrait { width: 120px; height: 120px; }
  .hero-portrait-wrap::before { display: none; }
  #hero { align-items: flex-start; padding-top: calc(var(--nav-h) + 48px); }
}

/* ── About / Skills ─────────────────────────────────────────── */
#about {
  background: var(--bg-alt);
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}

.about-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 64px;
  align-items: start;
}

.about-text p {
  color: var(--text-muted);
  font-size: 1rem;
  line-height: 1.8;
  margin-bottom: 16px;
}
.about-text p:last-child { margin-bottom: 0; }

.skills-grid {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 8px;
}

.skill-chip {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 5px 12px;
  font-family: var(--mono);
  font-size: 0.75rem;
  font-weight: 500;
  color: var(--text-muted);
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: 6px;
  transition: border-color var(--transition), color var(--transition), background var(--transition);
  letter-spacing: 0.02em;
}
.skill-chip:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-dim);
}
.skill-chip-dot {
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: var(--accent);
  flex-shrink: 0;
}

.skills-group-label {
  display: block;
  margin-bottom: 14px;
}

@media (max-width: 768px) {
  .about-grid { grid-template-columns: 1fr; gap: 40px; }
}

/* ── GitHub Stats ───────────────────────────────────────────── */
#stats {
  padding: 96px 0;
}

.stats-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
  margin-bottom: 20px;
}

.stats-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 24px;
  overflow: hidden;
  transition: border-color var(--transition), box-shadow var(--transition);
  display: flex;
  justify-content: center;
  align-items: center;
}
.stats-card:hover {
  border-color: var(--border-hover);
  box-shadow: var(--shadow-sm);
}

.stats-card img { max-width: 100%; height: auto; }

@media (max-width: 640px) {
  .stats-grid { grid-template-columns: 1fr; }
}

/* ── Projects ───────────────────────────────────────────────── */
#projects {
  background: var(--bg-alt);
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}

.projects-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
}

.project-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  transition: border-color var(--transition), transform var(--transition), box-shadow var(--transition);
  display: flex;
  flex-direction: column;
}
.project-card:hover {
  border-color: var(--border-hover);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.project-img-wrap {
  position: relative;
  overflow: hidden;
  background: var(--bg-alt);
  aspect-ratio: 16 / 9;
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}

.project-img-wrap img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  object-position: top;
  transition: transform 400ms cubic-bezier(.4,0,.2,1);
}
.project-card:hover .project-img-wrap img {
  transform: scale(1.03);
}

.project-body {
  padding: 24px;
  display: flex;
  flex-direction: column;
  flex: 1;
}

.project-tags {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  margin-bottom: 12px;
}

.project-tag {
  font-family: var(--mono);
  font-size: 0.6875rem;
  font-weight: 500;
  padding: 2px 8px;
  border-radius: 4px;
  background: var(--accent-dim);
  color: var(--accent);
  letter-spacing: 0.03em;
  text-transform: uppercase;
}

.project-title {
  font-size: 1rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 4px;
  line-height: 1.3;
}

.project-title-zh {
  font-size: 0.8125rem;
  color: var(--text-subtle);
  font-weight: 400;
  margin-bottom: 12px;
  font-family: var(--sans);
}

.project-desc {
  font-size: 0.875rem;
  color: var(--text-muted);
  line-height: 1.7;
  flex: 1;
  margin-bottom: 16px;
}

.project-desc-zh {
  font-size: 0.8125rem;
  color: var(--text-subtle);
  line-height: 1.7;
  margin-bottom: 20px;
}

.project-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 0.8125rem;
  font-weight: 600;
  color: var(--accent);
  margin-top: auto;
  transition: gap var(--transition);
}
.project-link:hover { gap: 10px; color: var(--accent-hover); }
.project-link svg { width: 14px; height: 14px; flex-shrink: 0; }

@media (max-width: 768px) {
  .projects-grid { grid-template-columns: 1fr; }
}

/* ── Blog ───────────────────────────────────────────────────── */
#blog { padding: 96px 0; }

.blog-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 48px;
  display: flex;
  align-items: center;
  gap: 40px;
  transition: border-color var(--transition), transform var(--transition), box-shadow var(--transition);
}
.blog-card:hover {
  border-color: var(--border-hover);
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}

.blog-icon {
  flex-shrink: 0;
  width: 64px;
  height: 64px;
  border-radius: var(--radius);
  background: var(--accent-dim);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--accent);
}
.blog-icon svg { width: 32px; height: 32px; }

.blog-content h3 {
  font-size: 1.25rem;
  margin-bottom: 8px;
}

.blog-content p {
  color: var(--text-muted);
  font-size: 0.9375rem;
  margin-bottom: 20px;
  line-height: 1.7;
}

.blog-topics {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 24px;
}

.blog-topic {
  font-family: var(--mono);
  font-size: 0.75rem;
  padding: 4px 10px;
  border-radius: 5px;
  background: var(--bg-alt);
  border: 1px solid var(--border);
  color: var(--text-muted);
  letter-spacing: 0.02em;
}

@media (max-width: 640px) {
  .blog-card { flex-direction: column; gap: 24px; padding: 32px 24px; align-items: flex-start; }
}

/* ── Connect ─────────────────────────────────────────────────── */
#connect {
  background: var(--bg-alt);
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}

.connect-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 16px;
}

.connect-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px 24px;
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 12px;
  transition: border-color var(--transition), transform var(--transition), box-shadow var(--transition);
  text-decoration: none;
}
.connect-card:hover {
  border-color: var(--border-hover);
  transform: translateY(-2px);
  box-shadow: var(--shadow-sm);
}

.connect-icon {
  width: 40px;
  height: 40px;
  border-radius: 8px;
  background: var(--bg-alt);
  border: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--text-muted);
  transition: border-color var(--transition), color var(--transition), background var(--transition);
}
.connect-card:hover .connect-icon {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-dim);
}
.connect-icon svg { width: 18px; height: 18px; }

.connect-label {
  font-size: 0.875rem;
  font-weight: 600;
  color: var(--text);
  line-height: 1.2;
}
.connect-sublabel {
  font-size: 0.8125rem;
  color: var(--text-muted);
}

.connect-email-img {
  max-width: 100%;
  height: auto;
  opacity: 0.85;
  transition: opacity var(--transition);
  margin-top: 4px;
}
.connect-card:hover .connect-email-img { opacity: 1; }

@media (max-width: 900px) {
  .connect-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 480px) {
  .connect-grid { grid-template-columns: 1fr; }
}

/* ── Footer ─────────────────────────────────────────────────── */
.footer {
  padding: 32px 0;
  border-top: 1px solid var(--border);
}

.footer-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
}

.footer-copy {
  font-size: 0.8125rem;
  color: var(--text-subtle);
}

.back-to-top {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 0.8125rem;
  font-weight: 500;
  color: var(--text-subtle);
  padding: 6px 12px;
  border: 1px solid var(--border);
  border-radius: 6px;
  transition: color var(--transition), border-color var(--transition), background var(--transition);
}
.back-to-top:hover {
  color: var(--text);
  border-color: var(--border-hover);
  background: var(--bg-alt);
}
.back-to-top svg { width: 14px; height: 14px; }

@media (max-width: 480px) {
  .footer-inner { flex-direction: column; align-items: flex-start; }
}

/* ── Fade-in on scroll ─────────────────────────────────────── */
.fade-in {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 500ms ease, transform 500ms ease;
}
.fade-in.visible {
  opacity: 1;
  transform: translateY(0);
}

/* Stagger utility */
.stagger-1 { transition-delay: 80ms; }
.stagger-2 { transition-delay: 160ms; }
.stagger-3 { transition-delay: 240ms; }
.stagger-4 { transition-delay: 320ms; }

/* ── Divider ─────────────────────────────────────────────────── */
.divider {
  height: 1px;
  background: var(--border);
  margin: 0;
}