/* ============================================================
   Qiyao Peng — Academic site
   Single stylesheet shared across all pages.
   Design notes: Inter sans-serif throughout; neutral grayscale
   with a single deep-navy accent; left sidebar holds bio &
   contact; right column holds page content. No decorative
   gradients, no card shadows, no animation.
   ============================================================ */

/* ---------- Reset ---------- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { -webkit-text-size-adjust: 100%; }

/* ---------- Tokens ---------- */
:root {
  --bg: #ffffff;
  --ink: #1f2937;          /* primary text */
  --ink-2: #4b5563;        /* secondary text */
  --ink-3: #6b7280;        /* tertiary / meta */
  --ink-4: #9ca3af;        /* placeholder */
  --rule: #e5e7eb;
  --rule-2: #f3f4f6;
  --accent: #1d3557;       /* deep navy */
  --accent-hover: #2c5481;
  --max: 1140px;
  --gutter: clamp(1.25rem, 3vw, 2.25rem);
  --sidebar-w: 260px;
  --content-pad-top: 3.25rem;
  --font: "Inter", ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  --mono: ui-monospace, "SF Mono", Menlo, Consolas, monospace;
}

/* ---------- Base ---------- */
html { font-size: 16px; }
body {
  font-family: var(--font);
  color: var(--ink);
  background: var(--bg);
  font-weight: 400;
  line-height: 1.6;
  font-feature-settings: "ss01", "cv05";
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}

a {
  color: var(--accent);
  text-decoration: none;
  border-bottom: 1px solid transparent;
  transition: border-color .15s ease, color .15s ease;
}
a:hover { color: var(--accent-hover); border-bottom-color: currentColor; }

::selection { background: var(--accent); color: #fff; }

p { margin: 0 0 .85em; }
strong { font-weight: 600; color: var(--ink); }
em { font-style: italic; }

/* ---------- Layout ---------- */
.wrap {
  max-width: var(--max);
  margin: 0 auto;
  padding: 0 var(--gutter);
}

.layout {
  display: grid;
  grid-template-columns: var(--sidebar-w) 1fr;
  gap: clamp(2rem, 5vw, 4.5rem);
  padding-top: var(--content-pad-top);
  padding-bottom: 5rem;
  align-items: start;
}

/* ---------- Header / Top Nav ---------- */
header.site {
  border-bottom: 1px solid var(--rule);
  background: var(--bg);
  position: sticky;
  top: 0;
  z-index: 50;
}
header.site .wrap {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
  gap: 1.5rem;
}
.brand {
  font-weight: 600;
  font-size: 1rem;
  color: var(--ink);
  letter-spacing: -0.01em;
  border-bottom: 0;
}
.brand:hover { color: var(--accent); border-bottom: 0; }
.brand .ch { color: var(--ink-3); font-weight: 400; margin-left: .25em; }

nav.primary ul { list-style: none; display: flex; gap: clamp(1rem, 2.5vw, 1.75rem); }
nav.primary a {
  color: var(--ink-2);
  font-size: .92rem;
  font-weight: 500;
  padding: .25rem 0;
  border-bottom: 0;
  position: relative;
}
nav.primary a:hover { color: var(--accent); border-bottom: 0; }
nav.primary a.active { color: var(--ink); }
nav.primary a.active::after {
  content: "";
  position: absolute;
  left: 0; right: 0; bottom: -22px;
  height: 2px;
  background: var(--accent);
}

/* ---------- Sidebar ---------- */
aside.sidebar {
  position: sticky;
  top: calc(64px + 3.25rem);
  align-self: start;
}
.photo {
  width: 100%;
  max-width: var(--sidebar-w);
  aspect-ratio: 1 / 1;
  object-fit: cover;
  border-radius: 4px;
  display: block;
  background: var(--rule-2);
  margin-bottom: 1.25rem;
}
.photo.placeholder {
  display: grid;
  place-items: center;
  color: var(--ink-4);
  font-size: .85rem;
  letter-spacing: .04em;
  text-transform: uppercase;
}

.bio-name {
  font-size: 1.35rem;
  font-weight: 600;
  letter-spacing: -0.015em;
  color: var(--ink);
  margin-bottom: .15rem;
  line-height: 1.2;
}
.bio-name .cn { color: var(--ink-3); font-weight: 400; margin-left: .25em; font-size: .95em; }
.bio-role {
  font-size: .9rem;
  color: var(--ink-2);
  margin-bottom: 1rem;
  line-height: 1.45;
}
.bio-affil {
  font-size: .85rem;
  color: var(--ink-3);
  line-height: 1.55;
  margin-bottom: 1.25rem;
}
.bio-affil .org { color: var(--ink-2); }

.contact-list { list-style: none; font-size: .85rem; }
.contact-list li { margin-bottom: .55rem; }
.contact-list a {
  color: var(--ink-2);
  border-bottom: 0;
  display: inline-flex;
  align-items: center;
  gap: .55rem;
}
.contact-list a:hover { color: var(--accent); border-bottom: 0; }
.contact-list svg { width: 14px; height: 14px; flex: none; color: var(--ink-3); }
.contact-list a:hover svg { color: var(--accent); }

.cv-link {
  display: inline-flex;
  align-items: center;
  gap: .5rem;
  margin-top: 1rem;
  padding: .55rem .9rem;
  background: var(--ink);
  color: #fff !important;
  font-size: .82rem;
  font-weight: 500;
  letter-spacing: .01em;
  border-radius: 3px;
  border-bottom: 0 !important;
}
.cv-link:hover { background: var(--accent); border-bottom: 0 !important; }

/* ---------- Main content typography ---------- */
main.content { min-width: 0; max-width: 720px; }

.page-title {
  font-size: 1.9rem;
  font-weight: 600;
  letter-spacing: -0.02em;
  color: var(--ink);
  margin-bottom: 1.75rem;
  line-height: 1.15;
}

h2.section-title {
  font-size: .78rem;
  font-weight: 600;
  letter-spacing: .12em;
  text-transform: uppercase;
  color: var(--ink-3);
  margin: 2.5rem 0 1rem;
  padding-bottom: .5rem;
  border-bottom: 1px solid var(--rule);
}
.page-title + h2.section-title { margin-top: 0; }

h3.subsec {
  font-size: 1rem;
  font-weight: 600;
  color: var(--ink);
  margin: 1.5rem 0 .5rem;
}

main.content p {
  color: var(--ink-2);
  font-size: .98rem;
  line-height: 1.7;
  margin-bottom: 1rem;
}
main.content p:last-child { margin-bottom: 0; }

main.content ul { list-style: none; }

/* ---------- Publications / list rows ---------- */
.list { list-style: none; }
.list > li {
  display: grid;
  grid-template-columns: 64px 1fr;
  gap: 1.25rem;
  padding: 1rem 0;
  border-top: 1px solid var(--rule);
  font-size: .94rem;
  line-height: 1.65;
  color: var(--ink-2);
}
.list > li:last-child { border-bottom: 1px solid var(--rule); }
.list > li .when {
  color: var(--ink-3);
  font-size: .82rem;
  font-variant-numeric: tabular-nums;
  letter-spacing: .02em;
  padding-top: .15rem;
}
.list > li .when .yr {
  display: block;
  color: var(--ink);
  font-weight: 600;
  font-size: .95rem;
  margin-bottom: .15rem;
}
.list > li .what .me { color: var(--ink); font-weight: 600; }
.list > li .what .title { color: var(--ink); }
.list > li .what .venue { color: var(--ink); font-style: italic; }
.list > li .what .meta {
  display: block;
  color: var(--ink-3);
  font-size: .82rem;
  margin-top: .25rem;
  font-style: italic;
}
.list > li .what .links { margin-top: .35rem; font-size: .82rem; }
.list > li .what .links a {
  margin-right: .9rem;
  color: var(--ink-3);
  border-bottom: 1px dotted var(--ink-4);
}
.list > li .what .links a:hover { color: var(--accent); border-bottom-color: var(--accent); }
.list > li .what .badge {
  display: inline-block;
  margin-left: .35rem;
  padding: 0 .5rem;
  font-size: .7rem;
  font-weight: 600;
  letter-spacing: .04em;
  text-transform: uppercase;
  color: var(--accent);
  background: rgba(29, 53, 87, .08);
  border-radius: 2px;
  vertical-align: 1px;
}

@media (max-width: 600px) {
  .list > li { grid-template-columns: 1fr; gap: .35rem; }
  .list > li .when .yr { display: inline; margin-right: .5rem; }
}

/* ---------- Inline meta row (research interests) ---------- */
.interests {
  display: flex;
  flex-wrap: wrap;
  gap: .45rem;
  margin: .75rem 0 1.5rem;
}
.interests span {
  font-size: .78rem;
  font-weight: 500;
  padding: .2rem .65rem;
  background: var(--rule-2);
  color: var(--ink-2);
  border-radius: 2px;
  letter-spacing: .01em;
}

/* ---------- Tag pills (skills) ---------- */
.tagrow { display: flex; flex-wrap: wrap; gap: .4rem; margin: .35rem 0 1rem; }
.tag {
  font-size: .82rem;
  color: var(--ink-2);
  padding: .2rem .6rem;
  border: 1px solid var(--rule);
  border-radius: 2px;
}
.tag strong { color: var(--ink); }

/* ---------- Footer ---------- */
footer.site {
  border-top: 1px solid var(--rule);
  padding: 1.5rem 0 2.5rem;
  font-size: .8rem;
  color: var(--ink-3);
}
footer.site .wrap {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
}

/* ---------- Responsive ---------- */
@media (max-width: 860px) {
  .layout {
    grid-template-columns: 1fr;
    gap: 2.5rem;
    padding-top: 2.25rem;
  }
  aside.sidebar { position: static; }
  .photo { max-width: 160px; }
  nav.primary a.active::after { bottom: -22px; }
  main.content { max-width: 100%; }
}

@media (max-width: 520px) {
  header.site .wrap { height: auto; padding-top: .9rem; padding-bottom: .9rem; flex-direction: column; align-items: flex-start; gap: .5rem; }
  nav.primary a.active::after { display: none; }
  .page-title { font-size: 1.6rem; }
}

/* Print-friendly */
@media print {
  header.site, footer.site, .cv-link { display: none; }
  body { color: #000; }
  a { color: #000; text-decoration: underline; }
}