/* ============================================================
   Zhihao Zhang — Personal Homepage
   Style: classic researcher (Karpathy / Danijar / Lilian Weng),
          with the discipline of restrained Apple-inspired details.
   ============================================================ */

/* ─────────── Design Tokens ─────────── */
:root {
  --bg:            #fcfcfc;
  --bg-card:       #ffffff;
  --bg-soft:       #f5f6f8;
  --nav-bg:        rgba(252, 252, 252, 0.78);
  --nav-bg-scrolled: rgba(252, 252, 252, 0.92);

  --text:          #1a1a1a;
  --text-2:        #3f3f46;
  --text-3:        #71717a;
  --text-4:        #a1a1aa;

  --border:        rgba(0, 0, 0, 0.08);
  --border-strong: rgba(0, 0, 0, 0.14);

  --accent:        #3b7fbd;
  --accent-hover:  #2b6fa8;
  --accent-soft:   rgba(59, 127, 189, 0.10);

  --highlight-bg: #fef3c7;
  --highlight-fg: #92400e;
  --highlight-border: #fcd34d;

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.04);
  --shadow-md: 0 8px 24px rgba(0, 0, 0, 0.06);

  --ease: cubic-bezier(0.4, 0, 0.2, 1);
  --ease-spring: cubic-bezier(0.34, 1.56, 0.64, 1);

  --container: 880px;
  --nav-h: 58px;
  --radius-sm: 8px;
  --radius:    12px;
  --radius-lg: 16px;
}

[data-theme="dark"] {
  --bg:            #0e0e10;
  --bg-card:       #18181b;
  --bg-soft:       #1c1c1f;
  --nav-bg:        rgba(14, 14, 16, 0.74);
  --nav-bg-scrolled: rgba(14, 14, 16, 0.9);

  --text:          #f4f4f5;
  --text-2:        #d4d4d8;
  --text-3:        #a1a1aa;
  --text-4:        #71717a;

  --border:        rgba(255, 255, 255, 0.08);
  --border-strong: rgba(255, 255, 255, 0.16);

  --accent:        #60a5fa;
  --accent-hover:  #93c5fd;
  --accent-soft:   rgba(96, 165, 250, 0.14);

  --highlight-bg: rgba(252, 211, 77, 0.12);
  --highlight-fg: #fcd34d;
  --highlight-border: rgba(252, 211, 77, 0.32);

  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
  --shadow-md: 0 8px 24px rgba(0, 0, 0, 0.4);
}

/* ─────────── Base ─────────── */
*, *::before, *::after { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: Charter, "Charter BT", "Source Serif 4", "Source Serif Pro",
               "Iowan Old Style", "Sitka Text", Cambria, Georgia,
               "Songti SC", "Noto Serif CJK SC", "PingFang SC", serif;
  font-size: 17px;
  line-height: 1.5;
  letter-spacing: 0;
  font-feature-settings: "kern" 1, "liga" 1, "calt" 1;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  transition: background-color 0.3s var(--ease), color 0.3s var(--ease);
}

p { margin: 0 0 10px; }
strong { font-weight: 700; color: var(--text); }

a {
  color: var(--accent);
  text-decoration: none;
  transition: color 0.15s var(--ease);
}
a:hover { color: var(--accent-hover); text-decoration: underline; text-underline-offset: 3px; text-decoration-thickness: 1px; }

::selection { background: var(--accent-soft); color: var(--text); }

/* ─────────── Navigation ─────────── */
.nav {
  position: sticky;
  top: 0;
  z-index: 100;
  height: var(--nav-h);
  background: var(--nav-bg);
  backdrop-filter: saturate(180%) blur(16px);
  -webkit-backdrop-filter: saturate(180%) blur(16px);
  border-bottom: 1px solid transparent;
  transition: background-color 0.25s var(--ease), border-color 0.25s var(--ease);
}
.nav.scrolled {
  background: var(--nav-bg-scrolled);
  border-bottom-color: var(--border);
}
.nav-inner {
  max-width: var(--container);
  height: 100%;
  margin: 0 auto;
  padding: 0 24px;
  display: flex;
  align-items: center;
  gap: 20px;
}
.nav-brand {
  color: var(--text);
  font-size: 16.5px;
  font-weight: 600;
  letter-spacing: 0;
  white-space: nowrap;
}
.nav-brand:hover { color: var(--text); opacity: 0.7; text-decoration: none; }

.nav-links {
  flex: 1;
  display: flex;
  justify-content: center;
  gap: 26px;
}
.nav-links a {
  color: var(--text-2);
  font-size: 15px;
  font-weight: 400;
  position: relative;
  padding: 4px 0;
  transition: color 0.15s var(--ease);
}
.nav-links a:hover { color: var(--text); text-decoration: none; }
.nav-links a.active { color: var(--text); font-weight: 500; }
.nav-links a.active::after {
  content: '';
  position: absolute;
  left: 0; right: 0;
  bottom: -4px;
  height: 2px;
  background: var(--accent);
  border-radius: 2px;
}

.theme-toggle {
  width: 30px;
  height: 30px;
  border-radius: 50%;
  border: 1px solid var(--border);
  background: transparent;
  color: var(--text-2);
  font-size: 12px;
  cursor: pointer;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s var(--ease);
}
.theme-toggle:hover {
  color: var(--text);
  border-color: var(--border-strong);
}

/* ─────────── Main ─────────── */
main {
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 24px;
}

/* ─────────── About ─────────── */
.about {
  display: grid;
  grid-template-columns: 1fr 200px;
  gap: 40px;
  align-items: start;
  padding: 48px 0 12px;
  scroll-margin-top: 64px;
}

.about-text h1 {
  margin: 0 0 4px;
  font-size: 32px;
  font-weight: 700;
  letter-spacing: -0.005em;
  line-height: 1.2;
}
.about-text h1 .zh {
  font-weight: 500;
  color: var(--text-2);
  margin-left: 8px;
  font-size: 0.85em;
  letter-spacing: 0;
}

.about-text .role {
  margin: 0 0 18px;
  color: #6f747c;
  font-size: 15px;
}

.about-text p {
  margin: 0 0 10px;
  font-size: 16.5px;
  line-height: 1.62;
  color: var(--text);
}

.about-text .contact a { font-weight: 500; }

/* Photo */
.about-photo {
  width: 200px;
  height: 200px;
  border-radius: 50%;
  overflow: hidden;
  background: var(--bg-soft);
  box-shadow:
    0 0 0 1px var(--border),
    0 8px 28px rgba(0, 0, 0, 0.10);
  transition: transform 0.4s var(--ease), box-shadow 0.4s var(--ease);
  justify-self: end;
  align-self: start;
}
.about-photo:hover {
  transform: translateY(-3px);
  box-shadow:
    0 0 0 1px var(--border-strong),
    0 14px 36px rgba(0, 0, 0, 0.14);
}
.about-photo img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  object-position: 50% 8%;
  display: block;
}

/* Social row */
.social {
  list-style: none;
  margin: 18px 0 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}
.social a {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 5px 12px;
  font-size: 13px;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--bg-card);
  color: var(--text-2);
  transition: all 0.18s var(--ease);
}
.social a:hover {
  color: var(--accent);
  border-color: var(--accent);
  background: var(--accent-soft);
  text-decoration: none;
  transform: translateY(-1px);
}
.social a i { font-size: 12px; }

/* ─────────── Sections ─────────── */
.section {
  padding: 20px 0 8px;
  scroll-margin-top: 72px;
}

.section h2 {
  margin: 0 0 14px;
  font-size: 23px;
  font-weight: 700;
  letter-spacing: 0;
  color: var(--text);
  position: relative;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--border);
}

.section p {
  font-size: 16.5px;
  line-height: 1.62;
}

#publications {
  padding-top: 34px;
}

/* ─────────── Research interests ─────────── */
.interests {
  list-style: none;
  margin: 8px 0 0;
  padding: 0;
}
.interests li {
  position: relative;
  padding: 4px 0 4px 22px;
  font-size: 15.5px;
  color: var(--text);
  line-height: 1.58;
}
.interests li::before {
  content: '▸';
  position: absolute;
  left: 4px;
  top: 4px;
  color: var(--accent);
  font-size: 13px;
}

/* ─────────── News ─────────── */
.news-list {
  list-style: none;
  margin: 0;
  padding: 0;
}
.news-list li {
  display: grid;
  grid-template-columns: 84px 1fr;
  gap: 14px;
  padding: 3px 0;
  font-size: 15px;
  align-items: baseline;
}
.news-list li.news-extra {
  display: none;
}
.news-list.expanded li.news-extra {
  display: grid;
  animation: fadeSlide 0.25s var(--ease);
}
.news-list time {
  color: var(--text-3);
  font-size: 14.5px;
  font-variant-numeric: tabular-nums;
  font-weight: 500;
  letter-spacing: 0.01em;
}
.news-list p {
  margin: 0;
  font-size: 16.5px;
  line-height: 1.62;
  color: var(--text);
}
.news-list em {
  font-style: normal;
  color: var(--accent);
  font-weight: 600;
}

.news-toggle {
  margin-top: 10px;
  background: none;
  border: none;
  padding: 4px 0;
  color: var(--accent);
  font-size: 13.5px;
  font-family: inherit;
  cursor: pointer;
  transition: color 0.15s var(--ease);
}
.news-toggle:hover { color: var(--accent-hover); text-decoration: underline; text-underline-offset: 3px; }

@keyframes fadeSlide {
  from { opacity: 0; transform: translateY(-2px); }
  to   { opacity: 1; transform: translateY(0); }
}

/* ─────────── Publications ─────────── */
.pubs {
  list-style: none;
  margin: 0;
  padding: 0;
}

.pub {
  display: grid;
  grid-template-columns: 168px 1fr;
  gap: 20px;
  padding: 10px 0;
  border-bottom: 1px solid var(--border);
  align-items: start;
  transition: background-color 0.2s var(--ease);
}
.pub:first-of-type { padding-top: 4px; }
.pub:last-of-type { border-bottom: none; padding-bottom: 4px; }
.pub:hover .pub-title { color: var(--accent); }

.pub-figure {
  display: block;
  width: 168px;
  height: 108px;
  border-radius: var(--radius-sm);
  overflow: hidden;
  background: var(--bg-soft);
  border: 1px solid var(--border);
  cursor: zoom-in;
}
.pub-figure img {
  width: 100%;
  height: 100%;
  object-fit: contain;
  padding: 4px;
  transition: transform 0.4s var(--ease);
}
.pub-figure:hover img { transform: scale(1.04); }

.pub-body {
  min-width: 0;
  display: flex;
  flex-direction: column;
  gap: 1.5px;
  padding-top: 2px;
}

.pub-title {
  margin: 0;
  font-size: 17px;
  font-weight: 400;
  line-height: 1.38;
  letter-spacing: 0;
  color: var(--text);
  transition: color 0.2s var(--ease);
}

.pub-title a strong {
  color: inherit;
  font-weight: inherit;
}

.pub-authors {
  margin: 2px 0 0;
  font-size: 15px;
  line-height: 1.48;
  color: var(--text-2);
}
.pub-authors strong { color: var(--text); font-weight: 600; }
.pub-authors a {
  color: var(--text-2);
  text-decoration: none;
}
.pub-authors a:hover {
  color: var(--accent);
  text-decoration: underline;
  text-underline-offset: 2px;
}
.equal { color: var(--text-3); font-weight: 600; }

.pub-links {
  margin: 2px 0 0;
  font-size: 15px;
  line-height: 1.48;
  color: var(--text-3);
}
.pub-links a {
  color: var(--accent);
  font-weight: 400;
}
.pub-links a:hover {
  text-decoration: underline;
  text-underline-offset: 2px;
}
.pub-links .link-separator {
  color: var(--text-4);
  margin: 0 0.45em;
}

.pub-venue {
  margin: 2px 0 0;
  font-size: 14.5px;
  line-height: 1.48;
}

.venue {
  font-style: italic;
  font-weight: 500;
  color: var(--text-2);
}

.highlight-marker {
  color: #dc2626;
  font-weight: 700;
}
[data-theme="dark"] .highlight-marker {
  color: #f87171;
}

.pub-footnote {
  margin: 16px 0 0;
  font-size: 13px;
  color: var(--text-3);
  font-style: italic;
}

/* ─────────── Timeline (Education / Experience) ─────────── */
.timeline {
  list-style: none;
  margin: 4px 0 0;
  padding: 0;
}
.timeline li {
  display: grid;
  grid-template-columns: 170px 1fr;
  gap: 16px;
  padding: 6px 0;
  font-size: 15px;
  line-height: 1.6;
  align-items: baseline;
  color: var(--text);
}
.timeline time {
  color: var(--text-3);
  font-size: 13.5px;
  font-variant-numeric: tabular-nums;
  font-weight: 500;
  letter-spacing: 0.01em;
  white-space: nowrap;
}

@media (max-width: 640px) {
  .timeline li {
    grid-template-columns: 1fr;
    gap: 1px;
    padding: 7px 0;
  }
  .timeline time { font-size: 12.5px; }
}

/* ─────────── Footer ─────────── */
.footer {
  margin-top: 56px;
  padding: 24px 24px 36px;
  border-top: 1px solid var(--border);
  text-align: center;
  color: var(--text-4);
  font-size: 12.5px;
}
.footer p { margin: 0; }

/* ─────────── Lightbox ─────────── */
#lightbox {
  position: fixed;
  inset: 0;
  z-index: 1000;
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  transition: opacity 0.2s var(--ease);
}
#lightbox.open { opacity: 1; }
#lightbox[hidden] { display: none; }
.lightbox-backdrop {
  position: absolute;
  inset: 0;
  background: rgba(0, 0, 0, 0.55);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
}
.lightbox-frame {
  position: relative;
  max-width: min(92vw, 920px);
  max-height: 90vh;
  background: var(--bg-card);
  border-radius: var(--radius-lg);
  padding: 20px;
  box-shadow: 0 30px 80px rgba(0, 0, 0, 0.4);
  transform: scale(0.96);
  transition: transform 0.25s var(--ease-spring);
  display: flex;
  align-items: center;
  justify-content: center;
}
#lightbox.open .lightbox-frame { transform: scale(1); }
#lightbox-img {
  display: block;
  max-width: 100%;
  max-height: calc(90vh - 80px);
  border-radius: var(--radius-sm);
}
#lightbox-close {
  position: absolute;
  top: 10px;
  right: 10px;
  width: 28px;
  height: 28px;
  border-radius: 50%;
  border: none;
  background: var(--bg-soft);
  color: var(--text);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 11px;
  transition: transform 0.18s var(--ease), background 0.18s var(--ease);
}
#lightbox-close:hover { transform: scale(1.08); }

/* ─────────── Responsive ─────────── */
@media (max-width: 720px) {
  .nav-inner { padding: 0 16px; gap: 12px; justify-content: space-between; }
  .nav-links { display: none; }
  .nav-brand { font-size: 15.5px; }

  main { padding: 0 16px; }

  .about {
    grid-template-columns: 1fr;
    gap: 24px;
    padding-top: 36px;
  }
  .about-photo {
    width: 140px;
    height: 140px;
    justify-self: center;
    order: -1;
  }
  .about-text h1 { font-size: 26px; text-align: center; }
  .about-text .role { text-align: center; }
  .social { justify-content: center; }

  .section { padding-top: 28px; }
  .section h2 { font-size: 20px; }

  .news-list li {
    grid-template-columns: 1fr;
    gap: 2px;
    padding: 8px 0;
    border-bottom: 1px dashed var(--border);
  }
  .news-list li:last-child { border-bottom: none; }

  .pub {
    grid-template-columns: 1fr;
    gap: 12px;
  }
  .pub-figure {
    width: 100%;
    max-width: 320px;
    height: 160px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
  html { scroll-behavior: auto; }
}