/* ==========================================================
   Xusheng Zhang — personal academic site
   Shared stylesheet for all pages.
   Accent colour: Durham purple. Change --accent to restyle.
   ========================================================== */

:root {
  --accent: #68246d;          /* Durham purple */
  --accent-dark: #4a1a4e;
  --accent-soft: #f4eef5;
  --text: #1f1f24;
  --muted: #5c5c66;
  --line: #e3e0e6;
  --bg: #ffffff;
  --bg-alt: #faf9fb;
  --link: #68246d;
  --maxw: 960px;
  --serif: "Source Serif 4", Georgia, "Times New Roman", serif;
  --sans: "Source Sans 3", -apple-system, "Segoe UI", Helvetica, Arial, sans-serif;
}

@media (prefers-color-scheme: dark) {
  :root {
    --accent: #b77fbd;
    --accent-dark: #2b1230;
    --accent-soft: #2a2230;
    --text: #e9e7ec;
    --muted: #a8a3ae;
    --line: #34303a;
    --bg: #17151a;
    --bg-alt: #1e1b22;
    --link: #d2a6d7;
  }
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--sans);
  font-size: 17px;
  line-height: 1.6;
  color: var(--text);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}
body > main { flex: 1 0 auto; }

a { color: var(--link); text-decoration: none; }
a:hover { text-decoration: underline; text-underline-offset: 2px; }

.skip-link {
  position: absolute; left: -9999px; top: 0;
  background: var(--accent); color: #fff; padding: 8px 12px; z-index: 10;
}
.skip-link:focus { left: 8px; }

.wrap { max-width: var(--maxw); margin: 0 auto; padding: 0 24px; }

/* ---------- Header / navigation ---------- */
.site-header {
  background: #68246d;
  color: #fff;
}
@media (prefers-color-scheme: dark) {
  .site-header { background: #3a1840; }
}
.site-header .wrap {
  display: flex; align-items: center; justify-content: space-between;
  gap: 16px; flex-wrap: wrap;
  min-height: 64px;
}
.site-title {
  font-family: var(--serif);
  font-size: 1.45rem; font-weight: 600; letter-spacing: .2px;
  color: #fff;
}
.site-title:hover { text-decoration: none; opacity: .9; }

.site-nav ul {
  list-style: none; margin: 0; padding: 0;
  display: flex; flex-wrap: wrap; gap: 4px;
}
.site-nav a {
  display: block; padding: 8px 14px; border-radius: 4px;
  color: #fff; font-weight: 600; font-size: .95rem; letter-spacing: .3px;
  opacity: .88;
}
.site-nav a:hover { background: rgba(255,255,255,.12); text-decoration: none; opacity: 1; }
.site-nav a[aria-current="page"] {
  opacity: 1; background: rgba(255,255,255,.18);
}

/* ---------- Page body ---------- */
main { padding: 48px 0 64px; }

h1, h2, h3 { font-family: var(--serif); font-weight: 600; line-height: 1.25; }
h1 { font-size: 2.1rem; margin: 0 0 .25em; }
h2 {
  font-size: 1.45rem; margin: 2.2em 0 .8em;
  padding-bottom: .35em; border-bottom: 2px solid var(--line);
  position: relative;
}
h2::after {
  content: ""; position: absolute; left: 0; bottom: -2px;
  width: 48px; height: 2px; background: var(--accent);
}
h3 { font-size: 1.12rem; margin: 1.6em 0 .5em; }
.h2-aside { font-family: var(--sans); font-size: .95rem; font-weight: 400; color: var(--muted); margin-left: 4px; }

.page-intro { color: var(--muted); margin-top: 0; }

/* ---------- Profile block (home page) ---------- */
.profile {
  display: grid;
  grid-template-columns: 260px 1fr;
  gap: 36px;
  align-items: start;
}
.profile-photo {
  width: 260px; height: 260px; object-fit: cover;
  border-radius: 6px; background: var(--accent-soft);
  border: 1px solid var(--line);
  display: block;
}
.profile .role { font-size: 1.12rem; margin: 0; font-weight: 600; }
.profile .affil { margin: 2px 0 0; color: var(--muted); }
.profile .affil a { color: var(--muted); border-bottom: 1px dotted currentColor; }
.profile .affil a:hover { text-decoration: none; color: var(--link); }

.contact { margin: 16px 0 0; padding: 0; list-style: none; }
.contact li { margin: 2px 0; }
.contact .label {
  display: inline-block; min-width: 64px;
  color: var(--muted); font-size: .9rem; text-transform: uppercase; letter-spacing: .6px;
}

.profile-links {
  display: flex; flex-wrap: wrap; gap: 8px; margin: 18px 0 0; padding: 0; list-style: none;
}
.profile-links a {
  display: inline-block; padding: 5px 12px;
  border: 1px solid var(--accent); border-radius: 999px;
  font-size: .9rem; font-weight: 600;
}
.profile-links a:hover { background: var(--accent); color: #fff; text-decoration: none; }

.bio p { margin: 0 0 1em; }

.interests {
  display: flex; flex-wrap: wrap; gap: 8px; list-style: none; padding: 0; margin: 0;
}
.interests li {
  background: var(--accent-soft); color: var(--text);
  padding: 4px 12px; border-radius: 4px; font-size: .95rem;
}

/* ---------- Research tree (home page) ---------- */
.research-intro { margin: 0 0 18px; }
.rtree { --tree: var(--accent); --gap: 14px; }
.rtree-root {
  position: relative; width: fit-content; max-width: 100%; margin: 0 auto;
  padding: 6px 16px; border-radius: 999px;
  background: var(--accent); color: var(--bg);
  font-family: var(--serif); font-weight: 600; font-size: 1.02rem; text-align: center;
}
.rtree-root::after {
  content: ""; position: absolute; left: 50%; bottom: calc(-1 * var(--gap)); height: var(--gap);
  border-left: 2px solid var(--tree);
}
.rtree-branches {
  position: relative;
  display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 16px;
  margin-top: calc(2 * var(--gap));
}
.rtree-branches::before {
  content: ""; position: absolute; top: calc(-1 * var(--gap)); left: calc((100% - 32px) / 6); right: calc((100% - 32px) / 6);
  border-top: 2px solid var(--tree);
}
.rtree-branch {
  position: relative; display: block;
  border: 1px solid var(--line); border-radius: 6px;
  padding: 10px 14px; background: var(--bg-alt); color: var(--text);
}
.rtree-branch:hover { border-color: var(--accent); text-decoration: none; }
.rtree-branch:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.rtree-branch::before {
  content: ""; position: absolute; left: 50%; top: calc(-1 * var(--gap) - 1px); height: var(--gap);
  border-left: 2px solid var(--tree);
}
.rtree-title { display: block; font-weight: 700; font-size: .95rem; color: var(--link); }
.rtree-sub { list-style: none; margin: 4px 0 0; padding: 0; font-size: .85rem; line-height: 1.5; color: var(--muted); }
.rtree-sub li { position: relative; padding-left: 12px; }
.rtree-sub li::before { content: ""; position: absolute; left: 1px; top: .62em; width: 5px; height: 5px; border-radius: 50%; background: var(--accent); opacity: .6; }

/* ---------- News ---------- */
.news { list-style: none; padding: 0; margin: 0; }
.news li {
  display: grid; grid-template-columns: 96px 1fr; gap: 16px;
  padding: 10px 0; border-bottom: 1px solid var(--line);
}
.news li:last-child { border-bottom: 0; }
.news time {
  font-variant-numeric: tabular-nums;
  color: var(--accent); font-weight: 700; font-size: .92rem; padding-top: 2px;
}
details.older { margin-top: 10px; }
details.older summary {
  cursor: pointer; color: var(--link); font-weight: 600; padding: 6px 0;
}

/* ---------- Publications ---------- */
.pub-meta { color: var(--muted); }
.pub-jump { display: flex; gap: 14px; flex-wrap: wrap; margin: 6px 0 0; font-weight: 600; }

ol.pubs { list-style: none; padding: 0; margin: 0; counter-reset: none; }
ol.pubs > li {
  display: grid; grid-template-columns: 44px 1fr; gap: 12px;
  padding: 16px 0; border-bottom: 1px solid var(--line);
}
ol.pubs > li:last-child { border-bottom: 0; }
.pub-num {
  font-family: var(--serif); color: var(--muted); font-size: 1.05rem; text-align: right;
  padding-top: 1px;
}
.pub-title { font-weight: 700; font-size: 1.04rem; line-height: 1.4; }
.pub-authors { color: var(--muted); margin-top: 2px; }
.pub-venue { margin-top: 4px; }
.pub-venue em { font-style: italic; }
.pub-venue .line { display: block; }
.pub-tag {
  display: inline-block; font-size: .78rem; font-weight: 700; letter-spacing: .4px;
  padding: 1px 7px; border-radius: 3px; margin-right: 6px; vertical-align: 1px;
  background: var(--accent-soft); color: var(--accent);
}
.pub-links { margin-top: 6px; display: flex; flex-wrap: wrap; gap: 6px; }
.pub-links a {
  font-size: .82rem; font-weight: 600; padding: 2px 9px;
  border: 1px solid var(--line); border-radius: 3px; color: var(--link);
}
.pub-links a:hover { border-color: var(--accent); text-decoration: none; background: var(--accent-soft); }

.note { color: var(--muted); font-size: .92rem; }

/* Publication topic filter */
.pub-filter { display: flex; flex-wrap: wrap; gap: 8px; margin: 0 0 12px; }
.pub-filter button {
  font: inherit; font-size: .92rem; font-weight: 600; cursor: pointer;
  padding: 6px 14px; border-radius: 999px;
  border: 1px solid var(--accent); background: transparent; color: var(--link);
}
.pub-filter button:hover { background: var(--accent-soft); }
.pub-filter button[aria-pressed="true"] { background: var(--accent); border-color: var(--accent); color: var(--bg); }
.pub-filter button:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }
.pub-filter .count { font-weight: 400; opacity: .8; margin-left: 2px; }
ol.pubs > li[hidden] { display: none; }

/* Selected publications on the home page: no numbers */
ol.pubs.selected > li { grid-template-columns: 1fr; padding: 14px 0; }
.more { margin: 10px 0 0; font-weight: 600; }

/* ---------- Service ---------- */
.svc-grid {
  display: grid; grid-template-columns: 1fr 1fr; gap: 24px;
}
.card {
  border: 1px solid var(--line); border-radius: 6px; padding: 18px 22px;
  background: var(--bg-alt);
}
.card h3 { margin-top: 0; }
.card ul { margin: 0; padding-left: 1.1em; }
.card li { margin: 4px 0; }
.card .years { color: var(--muted); }

/* ---------- CV ---------- */
.btn {
  display: inline-block; background: var(--accent); color: #fff;
  padding: 10px 20px; border-radius: 4px; font-weight: 700;
}
.btn:hover { background: var(--accent-dark); text-decoration: none; }
@media (prefers-color-scheme: dark) { .btn { color: #17151a; } .btn:hover { color: #fff; } }

.timeline { list-style: none; padding: 0; margin: 0; }
.timeline li {
  display: grid; grid-template-columns: 150px 1fr; gap: 16px;
  padding: 10px 0; border-bottom: 1px solid var(--line);
}
.timeline li:last-child { border-bottom: 0; }
.timeline .when { color: var(--muted); font-variant-numeric: tabular-nums; }
.timeline .what strong { display: block; }

/* ---------- Placeholder highlighting (remove .todo class once filled) ---------- */
.todo {
  background: repeating-linear-gradient(135deg, #fff7d6, #fff7d6 8px, #fff3c2 8px, #fff3c2 16px);
  color: #6b5200; border-radius: 3px; padding: 0 4px;
}
@media (prefers-color-scheme: dark) {
  .todo { background: #3a3218; color: #f0d98a; }
}

/* ---------- Footer ---------- */
.site-footer {
  border-top: 1px solid var(--line); background: var(--bg-alt);
  color: var(--muted); font-size: .9rem;
}
.site-footer .wrap {
  display: flex; justify-content: space-between; flex-wrap: wrap; gap: 8px;
  padding-top: 20px; padding-bottom: 20px;
}

/* ---------- Small screens ---------- */
@media (max-width: 720px) {
  body { font-size: 16px; }
  .wrap { padding: 0 16px; }
  .site-header .wrap { padding-top: 10px; padding-bottom: 10px; }
  .site-nav a { padding: 6px 10px; }
  main { padding: 32px 0 48px; }
  .profile { grid-template-columns: 1fr; gap: 20px; }
  .profile-photo { width: 200px; height: 200px; }
  h1 { font-size: 1.75rem; }
  .svc-grid { grid-template-columns: 1fr; }
  .news li { grid-template-columns: 1fr; gap: 0; }
  .timeline li { grid-template-columns: 1fr; gap: 0; }
  ol.pubs > li { grid-template-columns: 32px 1fr; gap: 8px; }
  /* research tree becomes a vertical outline */
  .rtree-root { margin: 0; }
  .rtree-root::after { left: 22px; }
  .rtree-branches { grid-template-columns: 1fr; gap: 10px; margin-top: var(--gap); margin-left: 23px; padding-left: 16px; border-left: 2px solid var(--tree); }
  .rtree-branches::before { display: none; }
  .rtree-branch::before { left: -17px; top: 18px; height: 0; width: 16px; border-left: 0; border-top: 2px solid var(--tree); }
  .rtree-branch:last-child::after { content: ""; position: absolute; left: -21px; top: 20px; bottom: -2px; width: 6px; background: var(--bg); }
}

/* keep superscripts from stretching line height */
sup { line-height: 0; }