/* =========================================================
   Ken (Tongli) Su — personal website
   Plain CSS. Light palette on :root, dark overrides on html.dark.
   ========================================================= */

:root {
  --bg: #ffffff;
  --bg-soft: #f8fafc;
  --card: #ffffff;
  --text: #1e2229;
  --muted: #64748b;
  --accent: #1f3864;          /* same navy as the CV */
  --accent-2: #0ea5e9;        /* cyan end of the gradient */
  --accent-3: #6366f1;        /* indigo accent */
  --button-bg: #1f3864;
  --button-text: #ffffff;
  --accent-soft: #eef3fb;
  --border: #e5e9ef;
  --tag-bg: #f1f5f9;
  --tag-text: #475569;
  --badge-grad: linear-gradient(135deg, #1f3864, #2f6fb5);
  --shadow: 0 10px 30px rgba(15, 23, 42, .10);
  --shadow-sm: 0 3px 12px rgba(15, 23, 42, .06);
  --max-width: 1000px;
  --radius: 14px;
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial,
          "Noto Sans", "PingFang SC", "Microsoft YaHei", sans-serif;
}

html.dark {
  --bg: #0f1216;
  --bg-soft: #151a21;
  --card: #161b22;
  --text: #e6e9ee;
  --muted: #94a3b8;
  --accent: #7fb0f2;
  --accent-2: #38d0ee;
  --accent-3: #8b8cf9;
  --button-bg: #7fb0f2;
  --button-text: #0f1216;
  --accent-soft: #18222f;
  --border: #262d37;
  --tag-bg: #1b222c;
  --tag-text: #b4c0cf;
  --badge-grad: linear-gradient(135deg, #2f4a78, #3b7fbf);
  --shadow: 0 10px 30px rgba(0, 0, 0, .45);
  --shadow-sm: 0 3px 12px rgba(0, 0, 0, .3);
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }
a:focus-visible, button:focus-visible { outline: 2px solid var(--accent); outline-offset: 4px; }
html { scroll-behavior: smooth; scroll-padding-top: 76px; }

body {
  margin: 0;
  font-family: var(--font);
  font-size: 16px;
  line-height: 1.68;
  color: var(--text);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
}

a { color: var(--accent); text-decoration: none; }
a:hover { text-decoration: underline; }

.container { max-width: var(--max-width); margin: 0 auto; padding: 0 24px 72px; }
@media (min-width: 781px) { #top > .container { padding-bottom: 20px; } }

/* ===================== NAV ===================== */
.nav {
  position: sticky; top: 0; z-index: 40;
  background: color-mix(in srgb, var(--bg) 82%, transparent);
  backdrop-filter: saturate(180%) blur(12px);
  border-bottom: 1px solid var(--border);
}
.scroll-progress {
  height: 2px; width: 0%;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  transition: width .1s linear;
}
.nav-inner {
  max-width: var(--max-width); margin: 0 auto;
  display: flex; justify-content: space-between; align-items: center;
  gap: 16px; padding: 12px 24px;
}
.nav .logo a { font-size: 15.5px; font-weight: 750; color: var(--text); letter-spacing: -.02em; }
.nav .logo a:hover { text-decoration: none; }
.logo-dot {
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text; background-clip: text; color: transparent;
}
.menu {
  display: flex; align-items: center; flex-wrap: wrap;
  gap: 4px 18px; list-style: none; margin: 0; padding: 0;
}
.menu a { position: relative; color: var(--muted); font-size: 14px; font-weight: 500; }
.menu a::after {
  content: ""; position: absolute; left: 0; right: 0; bottom: -5px; height: 2px; border-radius: 2px;
  background: linear-gradient(90deg, var(--accent), var(--accent-2));
  transform: scaleX(0); transform-origin: left; transition: transform .2s ease;
}
.menu a:hover::after, .menu a.active::after { transform: scaleX(1); }
.menu a:hover, .menu a.active { color: var(--text); text-decoration: none; }

#theme-toggle {
  background: none; border: none; cursor: pointer; padding: 10px; margin: -10px; color: var(--text);
  display: inline-flex; align-items: center; transition: transform .2s ease, color .2s ease;
}
#theme-toggle:hover { color: var(--accent); transform: rotate(18deg) scale(1.1); }
#theme-toggle svg { width: 17px; height: 17px; }
html.dark #theme-toggle .moon { display: none; }
html:not(.dark) #theme-toggle .sun { display: none; }

/* ===================== HERO ===================== */
header.profile {
  display: flex; gap: 40px; align-items: center; padding: 62px 0 34px;
}

.photo-ring { flex: 0 0 auto; }
.photo {
  display: block; width: 176px; height: 176px; border-radius: 50%;
  object-fit: cover; background: var(--bg-soft);
}

.eyebrow {
  margin: 0 0 6px; font-size: 12.5px; font-weight: 700; letter-spacing: .12em;
  text-transform: uppercase; color: var(--muted);
}
.intro h1 {
  margin: 0 0 6px; font-size: 40px; line-height: 1.15; letter-spacing: -.03em;
  font-weight: 780; color: #000;
}
html.dark .intro h1 { color: var(--text); }
.intro .tagline { margin: 0 0 18px; font-size: 15.5px; color: var(--muted); }

.links { display: flex; flex-wrap: wrap; gap: 9px; }
.links a {
  display: inline-flex; align-items: center; gap: 7px;
  font-size: 13.5px; font-weight: 600; padding: 7px 15px;
  border: 1px solid var(--border); border-radius: 999px;
  color: var(--text); background: var(--card);
  box-shadow: var(--shadow-sm);
  transition: transform .16s ease, box-shadow .16s ease, border-color .16s ease, color .16s ease;
}
.links a:hover {
  text-decoration: none; color: var(--accent); border-color: var(--accent);
  transform: translateY(-2px); box-shadow: var(--shadow);
}
.links a.link-primary {
  color: var(--button-text); border-color: transparent;
  background: var(--button-bg);
}
.links a.link-primary:hover { color: var(--button-text); }
.links svg { width: 15px; height: 15px; }

/* ===================== SECTIONS ===================== */
section { padding-top: 40px; }
section h2 {
  display: flex; align-items: center; gap: 10px;
  font-size: 20px; letter-spacing: -.02em; font-weight: 720; margin: 0 0 18px;
}
.h-bar {
  width: 4px; height: 20px; border-radius: 3px;
  background: linear-gradient(180deg, var(--accent), var(--accent-2));
}
.bio { padding-top: 8px; }
.bio p { margin: 0 0 12px; }
.bio .cta { color: var(--muted); font-size: 15px; }

/* Content is visible by default, including when JavaScript is unavailable. */

/* ===================== RESEARCH CARDS ===================== */
.cards { display: grid; grid-template-columns: repeat(3, 1fr); gap: 16px; }
.research-card {
  position: relative; overflow: hidden;
  border: 1px solid var(--border); border-radius: var(--radius);
  padding: 20px; background: var(--bg-soft);
  transition: transform .2s ease, box-shadow .2s ease, border-color .2s ease;
}
.research-card:hover {
  transform: translateY(-4px);
  box-shadow: var(--shadow);
  border-color: var(--accent);
}
.rc-icon {
  width: 38px; height: 38px; border-radius: 10px; margin-bottom: 12px;
  display: flex; align-items: center; justify-content: center;
  background: var(--accent-soft); color: var(--accent);
}
.rc-icon svg { width: 20px; height: 20px; }
.research-card h3 { margin: 0 0 7px; font-size: 15.5px; font-weight: 680; }
.research-card p { margin: 0; font-size: 14.2px; color: var(--muted); line-height: 1.6; }

/* ===================== NEWS ===================== */
.news-list { list-style: none; margin: 0; padding: 0 0 0 2px; }
.news-list li {
  position: relative; display: flex; gap: 16px;
  padding: 9px 0 9px 22px; font-size: 14.8px;
  border-left: 2px solid var(--border);
}
.news-list li::before {
  content: ""; position: absolute; left: -5px; top: 18px;
  width: 8px; height: 8px; border-radius: 50%;
  background: var(--bg); border: 2px solid var(--accent);
  transition: transform .2s ease, background .2s ease;
}
.news-list li:hover::before { transform: scale(1.35); background: var(--accent); }
.news-list li:first-child::before {
  background: linear-gradient(135deg, var(--accent), var(--accent-2)); border-color: transparent;
  box-shadow: 0 0 0 4px var(--accent-soft);
}
.news-date { flex: 0 0 66px; color: var(--muted); font-size: 13.6px; font-variant-numeric: tabular-nums; }
.more-btn {
  margin-top: 14px; font: inherit; font-size: 13.5px; font-weight: 600;
  color: var(--accent); background: var(--card); border: 1px solid var(--border);
  border-radius: 999px; padding: 6px 16px; cursor: pointer; transition: all .16s ease;
}
.more-btn:hover { border-color: var(--accent); background: var(--accent-soft); transform: translateY(-1px); }

/* ===================== PUBLICATIONS ===================== */
.pubs { display: flex; flex-direction: column; gap: 18px; }
#publications h2 { font-size: 23px; }
.pub {
  display: flex; gap: 20px; align-items: flex-start;
  padding: 22px 24px; border: 1px solid var(--border); border-radius: 10px;
  border-left: 3px solid var(--accent);
  background: var(--card);
  transition: transform .2s ease, box-shadow .2s ease, border-color .2s ease, opacity .25s ease;
}
.pub:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow);
  border-color: var(--accent);
}

.pub-thumb {
  flex: 0 0 152px; height: 96px; border-radius: 10px; overflow: hidden;
  border: 1px solid var(--border);
  background: linear-gradient(135deg, var(--accent-soft), var(--tag-bg));
  display: flex; align-items: center; justify-content: center;
}
.pub-thumb img { width: 100%; height: 100%; object-fit: contain; display: block; }
.pub-body { flex: 1; min-width: 0; }
.pub-title { margin: 0 0 4px; font-size: 17px; font-weight: 680; line-height: 1.45; }
.pub-title a { color: var(--text); }
.pub-title a:hover { color: var(--accent); text-decoration: none; }
.pub-authors { margin: 0 0 4px; font-size: 14px; color: var(--muted); }
.pub-author-note { margin: 0 0 6px; font-size: 12px; color: var(--muted); }
.pub-authors .me { color: var(--text); font-weight: 750; }
.pub-venue { margin: 0 0 8px; font-size: 14px; color: var(--muted); }
.pub-venue .venue-name { color: var(--text); font-style: italic; }
.badge {
  display: inline-block; margin-left: 7px; padding: 2px 9px; border-radius: 5px;
  font-size: 11.3px; font-weight: 700; letter-spacing: .03em; vertical-align: 1px;
  background: var(--badge-grad); color: #fff;
}
.badge.soft { background: var(--tag-bg); color: var(--tag-text); }
.pub-insight { margin: 0 0 12px; font-size: 15px; color: var(--text); line-height: 1.6; }
.pub-links { display: flex; flex-wrap: wrap; gap: 7px; }
.pub-links a {
  font-size: 12.4px; font-weight: 650; padding: 3px 12px; border-radius: 999px;
  border: 1px solid var(--border); color: var(--muted); transition: all .16s ease;
}
.pub-links a:hover {
  text-decoration: none; color: var(--button-text); border-color: transparent;
  background: var(--button-bg);
}

/* ===================== ROWS (education / experience) ===================== */
.row {
  display: flex; gap: 18px; align-items: center;
  padding: 18px 20px; margin-bottom: 10px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  background: var(--card);
  transition: transform .2s ease, box-shadow .2s ease, background-color .2s ease;
}
.row:hover {
  transform: translateY(-3px);
  box-shadow: var(--shadow-sm);
  background: var(--card);
}
.row:last-child { margin-bottom: 0; }
.row-logo {
  flex: 0 0 auto; width: 54px; height: 54px; border-radius: 12px; padding: 7px;
  display: flex; align-items: center; justify-content: center; overflow: hidden;
  background: #fff; border: 1px solid var(--border);
}
.row-logo img { max-width: 100%; max-height: 100%; object-fit: contain; display: block; }
/* horizontal wordmarks (e.g. DuPont) need the full width of the box */
.row-logo.wide { padding: 3px; }
.row-logo.wide img { width: 100%; }
.row-main { flex: 1; min-width: 0; }
.row-main .role { font-size: 15.4px; font-weight: 680; }
.row-main .org { font-size: 14.2px; color: var(--accent); font-weight: 600; }
.row-main .detail { font-size: 13.8px; color: var(--muted); line-height: 1.55; margin-top: 2px; }
.row .date {
  flex: 0 0 auto; text-align: right; font-size: 13.3px; color: var(--muted); white-space: nowrap;
}
.row .date span { display: block; font-size: 12.6px; opacity: .8; }

/* ===================== SERVICE ===================== */
.service-list { list-style: none; margin: 0; padding: 0; }
.service-list li { padding: 7px 0; font-size: 14.8px; }
.tag {
  display: inline-block; margin-right: 9px; padding: 2px 10px; border-radius: 5px;
  font-size: 12px; font-weight: 680; background: var(--tag-bg); color: var(--tag-text);
}

/* ===================== FOOTER / BACK TO TOP ===================== */
.site-footer {
  margin-top: 60px; padding-top: 20px; border-top: 1px solid var(--border);
  font-size: 13px; color: var(--muted); text-align: center;
}
.site-footer p { margin: 0; }

.to-top {
  position: fixed; right: 26px; bottom: 26px; z-index: 30;
  width: 42px; height: 42px; border-radius: 50%; border: none; cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  color: var(--button-text); background: var(--button-bg);
  box-shadow: var(--shadow);
  opacity: 0; visibility: hidden; transform: translateY(10px);
  transition: opacity .25s ease, transform .25s ease, visibility .25s;
}
.to-top.show { opacity: 1; visibility: visible; transform: none; }
.to-top:hover { transform: translateY(-3px) scale(1.05); }
.to-top svg { width: 18px; height: 18px; }

/* ===================== RESPONSIVE ===================== */
@media (max-width: 900px) {
  .cards { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 780px) {
  .nav-inner { padding: 10px 16px; flex-direction: column; align-items: flex-start; gap: 7px; }
  .menu { gap: 4px 14px; }
  .container { padding: 0 18px 56px; }
  header.profile { flex-direction: column; text-align: center; gap: 22px; padding: 36px 0 24px; }
  .photo { width: 146px; height: 146px; }
  .intro h1 { font-size: 31px; }
  .links { justify-content: center; }
  .cards { grid-template-columns: 1fr; }
  .pub { flex-direction: column; gap: 14px; }
  .pub-thumb { flex: none; width: 100%; height: 140px; }
  .row { flex-wrap: wrap; gap: 14px; }
  .row .date { flex-basis: 100%; text-align: left; padding-left: 72px; margin-top: -8px; }
  .row .date span { display: inline; }
  .row .date span::before { content: " · "; }
  .to-top { right: 16px; bottom: 16px; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  .research-card:hover, .pub:hover, .row:hover { transform: none; }
  * { transition-duration: .01ms !important; }
}

@media print {
  .nav, .to-top, #theme-toggle, .more-btn { display: none; }
  body { font-size: 12px; }
}