/* ============================================================
   Diandian Peng — personal site styles (self-contained, no framework)
   ============================================================ */

:root {
  --accent: #2a4d75;
  --accent-2: #3a6ea5;
  --accent-soft: #eef3f9;
  --ink: #1d2733;
  --muted: #5d6b7c;
  --border: #e6ebf1;
  --bg: #ffffff;
  --bg-soft: #f6f8fb;
  --radius: 14px;
  --page-max: 960px; /* one content width for every page */
  --shadow: 0 6px 24px rgba(20, 40, 70, 0.08);
  --shadow-lg: 0 14px 38px rgba(20, 40, 70, 0.14);
  --serif: "Source Serif 4", Georgia, "Times New Roman", serif;
  --sans: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

*, *::before, *::after { box-sizing: border-box; }
html { font-size: 18px; -webkit-text-size-adjust: 100%; scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--sans);
  color: var(--ink);
  background: var(--bg);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
img { max-width: 100%; height: auto; display: block; }
h1, h2, h3, h4 {
  font-family: var(--serif);
  line-height: 1.2;
  letter-spacing: -0.01em;
  color: var(--ink);
}
a { color: var(--accent); text-decoration: none; }
a:hover { color: var(--accent-2); text-decoration: underline; }

.container { max-width: var(--page-max); margin: 0 auto; padding: 0 1.25rem; }
.narrow { max-width: var(--page-max); }

/* ---- Header / nav ---- */
.site-header {
  position: sticky; top: 0; z-index: 50;
  background: rgba(255, 255, 255, 0.92);
  -webkit-backdrop-filter: saturate(180%) blur(8px);
  backdrop-filter: saturate(180%) blur(8px);
  border-bottom: 1px solid var(--border);
}
.site-nav {
  display: flex; align-items: center; justify-content: space-between;
  gap: 1.5rem; padding: 0.85rem 1.25rem; max-width: var(--page-max); margin: 0 auto;
}
.site-nav__brand {
  font-family: var(--serif); font-weight: 600; font-size: 1.32rem;
  color: var(--accent); text-decoration: none;
}
.site-nav__brand:hover { text-decoration: none; }
.site-nav__links { display: flex; gap: 1.6rem; list-style: none; margin: 0; padding: 0; }
.site-nav__links a {
  font-weight: 500; font-size: 0.98rem; color: var(--ink); text-decoration: none;
}
.site-nav__links a:hover, .site-nav__links a[aria-current="page"] { color: var(--accent); }

/* ---- Hero ---- */
.hero { padding: 3.2rem 0 1.4rem; }
.hero__inner { display: flex; gap: 2.6rem; align-items: center; }
.hero__photo {
  flex: 0 0 auto; width: 200px; height: 200px;
  border-radius: 50%; object-fit: cover;
  box-shadow: var(--shadow); border: 4px solid #fff;
}
.hero__body { min-width: 0; }
.eyebrow {
  text-transform: uppercase; letter-spacing: 0.13em; font-size: 0.72rem;
  font-weight: 600; color: var(--accent); margin: 0 0 0.45rem;
}
.hero__name { font-size: 2.8rem; margin: 0 0 0.55rem; }
.hero__lead { font-size: 1.12rem; color: var(--muted); margin: 0 0 1.3rem; max-width: 38em; }
.hero__actions { display: flex; flex-wrap: wrap; gap: 0.6rem; margin-bottom: 0.95rem; }
.profile-links { display: flex; flex-wrap: wrap; gap: 0.35rem 1.1rem; font-size: 0.92rem; }
.profile-links a { color: var(--muted); font-weight: 500; }
.profile-links a:hover { color: var(--accent); }

/* ---- Buttons ---- */
.btn {
  display: inline-block; padding: 0.5rem 1.1rem; border-radius: 999px;
  border: 1px solid var(--border); background: #fff; color: var(--ink);
  font-size: 0.92rem; font-weight: 500; text-decoration: none;
  transition: all 0.15s ease; cursor: pointer;
}
.btn:hover { border-color: var(--accent); color: var(--accent); text-decoration: none; transform: translateY(-1px); }
.btn--solid { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn--solid:hover { background: var(--accent-2); border-color: var(--accent-2); color: #fff; }

/* ---- Generic content sections ---- */
main { padding-bottom: 3.5rem; }
.section { padding-top: 1rem; }
.section h2 {
  font-size: 1.7rem; margin: 2.4rem 0 1.1rem;
  padding-bottom: 0.4rem; border-bottom: 1px solid var(--border);
}
.section h3 { font-size: 1.2rem; margin: 1.6rem 0 0.4rem; }
p { color: #34414f; }

/* ---- Callout / note ---- */
.note {
  background: var(--accent-soft); border: 1px solid #dbe6f2; border-radius: 12px;
  padding: 0.85rem 1.15rem; margin: 1.5rem 0; font-size: 0.97rem; color: var(--ink);
}
.note code { background: #fff; padding: 0.05em 0.35em; border-radius: 5px; font-size: 0.92em; }

/* ---- Section intro ---- */
.section__intro { font-size: 1.06rem; color: #34414f; margin: 0 0 2.2rem; }

/* ---- Research features (figure + text, alternating) ---- */
.features { display: flex; flex-direction: column; gap: 2.8rem; }
.feature { display: flex; gap: 2.2rem; align-items: center; scroll-margin-top: 90px; }
.feature--reverse { flex-direction: row-reverse; }
.feature__media { flex: 0 0 46%; }
.feature__media img {
  width: 100%; height: auto; border-radius: 12px;
  border: 1px solid var(--border); background: #eef2f6;
}
.feature__body { flex: 1; min-width: 0; }
.feature__body h3 { font-size: 1.35rem; margin: 0 0 0.6rem; }
.feature__body p { margin: 0 0 0.7rem; color: #34414f; }
.feature__ref { margin: 0.4rem 0 0; }
.feature__ref a { font-size: 0.9rem; font-weight: 600; }

/* "see publications" line on the Research page */
.research-more { margin: 2.4rem 0 0; color: #34414f; }

/* model animation videos (home) */
.video-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 1.4rem; }
.video-fig { margin: 0; }
.video-fig video { width: 100%; height: auto; display: block; border-radius: 12px; border: 1px solid var(--border); background: #52576e; }
.video-fig figcaption { margin-top: 0.55rem; color: var(--muted); font-size: 0.92rem; text-align: center; }
.video-note { color: var(--muted); font-size: 0.9rem; margin: 0.8rem 0 0; text-align: center; }
.research-sub { font-family: var(--serif); font-weight: 600; font-size: 1.18rem; margin: 2rem 0 0.9rem; }
@media (max-width: 640px) { .video-grid { grid-template-columns: 1fr; } }

/* compact research teaser (home page) */
.research-teaser { list-style: none; margin: 0 0 1.5rem; padding: 0; display: grid; grid-template-columns: 1fr 1fr; gap: 1rem 2rem; }
.research-teaser li { line-height: 1.4; }
.research-teaser a { font-family: var(--serif); font-weight: 600; font-size: 1.08rem; }
.research-teaser span { display: block; color: var(--muted); font-size: 0.93rem; margin-top: 0.15rem; }
@media (max-width: 640px) { .research-teaser { grid-template-columns: 1fr; gap: 0.9rem; } }

/* ---- Publications ---- */
.pub-group { margin-bottom: 2.2rem; }
.pub { padding: 1.15rem 0; border-bottom: 1px solid var(--border); }
.pub:last-child { border-bottom: none; }
.pub__title { font-family: var(--serif); font-size: 1.16rem; font-weight: 600; margin: 0 0 0.3rem; }
.pub__meta { color: var(--muted); font-size: 0.92rem; margin: 0 0 0.5rem; }
.pub__cite { font-size: 0.95rem; color: #3c4856; margin: 0 0 0.4rem; }
.pub__links a { font-size: 0.9rem; font-weight: 600; }
.pub__title .star { color: var(--accent); font-weight: 700; }
.pub-legend { color: var(--muted); font-size: 0.9rem; }

/* ---- Talks ---- */
.talk { padding: 1.1rem 0; border-bottom: 1px solid var(--border); }
.talk:last-child { border-bottom: none; }
.talk__title { font-family: var(--serif); font-size: 1.16rem; font-weight: 600; margin: 0 0 0.25rem; }
.talk__meta { color: var(--muted); font-size: 0.93rem; margin: 0; }
.talk__date { color: var(--accent); font-weight: 600; }

/* ---- CV ---- */
.cv-section { margin: 1.8rem 0; }
.cv-section h2 {
  font-size: 1.5rem; margin: 2.2rem 0 0.9rem;
  padding-bottom: 0.35rem; border-bottom: 1px solid var(--border);
}
.cv-list { margin: 0.5rem 0; padding-left: 1.2rem; }
.cv-list li { margin: 0.3rem 0; }
.cv-list ul { margin: 0.3rem 0; }
.cv-intro { font-size: 1.04rem; color: #34414f; margin: 0 0 1.1rem; }

/* date-aligned (timeline) CV entries */
.cv-entry { display: grid; grid-template-columns: 150px 1fr; gap: 1.4rem; margin: 0.95rem 0; }
.cv-entry__date { color: var(--muted); font-size: 0.9rem; padding-top: 0.1rem; }
.cv-entry__body p { margin: 0; }
.cv-entry__body p + p { margin-top: 0.3rem; }
.cv-entry__role { font-weight: 600; color: var(--ink); }
.cv-entry__org { color: var(--muted); }
.cv-entry__note { color: #3c4856; font-size: 0.95rem; }
.cv-entry__detail { margin: 0.45rem 0 0; padding-left: 1.1rem; color: #3c4856; font-size: 0.96rem; }
.cv-entry__detail li { margin: 0.22rem 0; }
@media (max-width: 640px) {
  .cv-entry { grid-template-columns: 1fr; gap: 0.2rem; }
  .cv-entry__date { padding-top: 0; font-weight: 600; color: var(--accent); }
}

/* ---- CTA row ---- */
.cta-row { display: flex; flex-wrap: wrap; gap: 0.7rem; margin: 1.8rem 0 0; }

/* ---- Footer ---- */
.site-footer {
  background: var(--bg-soft); border-top: 1px solid var(--border);
  padding: 1.6rem 0; margin-top: 2rem;
}
.site-footer .container { display: flex; flex-wrap: wrap; gap: 0.4rem 1.2rem; justify-content: space-between; align-items: center; }
.site-footer, .site-footer a { color: var(--muted); font-size: 0.85rem; }
.site-footer a:hover { color: var(--accent); }

/* ---- Skip link (accessibility) ---- */
.skip-link {
  position: absolute; left: -999px; top: 0; z-index: 100;
  background: var(--accent); color: #fff; padding: 0.5rem 1rem; border-radius: 0 0 8px 0;
}
.skip-link:focus { left: 0; text-decoration: none; }

/* ---- Responsive ---- */
@media (max-width: 768px) {
  html { font-size: 17px; }
  .hero { padding-top: 2.3rem; }
  .hero__inner { flex-direction: column; text-align: center; gap: 1.5rem; }
  .hero__photo { width: 158px; height: 158px; }
  .hero__name { font-size: 2.2rem; }
  .hero__lead { margin-left: auto; margin-right: auto; }
  .hero__actions, .profile-links { justify-content: center; }
  .feature, .feature--reverse { flex-direction: column; gap: 1.1rem; }
  .feature__media { flex: 1 1 auto; width: 100%; }
  .site-nav { flex-wrap: wrap; gap: 0.4rem 1.3rem; }
}