/* ------------------------------------------------------------------
   Xiaosong Yuan — Personal Homepage
   Design: minimalist academic, refined typography, hairline dividers.
   Palette: warm paper / deep slate, single muted gold accent.
------------------------------------------------------------------ */

:root {
  --bg:          #ffffff;
  --bg-elev:    #ffffff;
  --bg-soft:    #f8fafc;
  --text:        #1a1d22;
  --text-soft:  #4a525c;
  --text-mute:  #828a94;
  --rule:        #e5e7eb;
  --rule-soft:   #f1f3f5;
  --accent:      #8c6a3d;        /* muted antique gold */
  --accent-soft: #c9a96a;
  --link:        #1f3a5f;        /* deep ink blue */
  --link-hover:  #0e2238;
  --badge-bg:    #f0ece1;
  --badge-fg:    #6b5430;
  --pub-badge-bg: #e8f0fa;
  --pub-badge-fg: #1e4a8a;
  --pub-highlight-bg: #2563eb;
  --pub-highlight-fg: #ffffff;
  --shadow:      0 1px 2px rgba(20, 22, 28, .04), 0 8px 24px -16px rgba(20, 22, 28, .08);

  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Helvetica Neue', Arial, 'PingFang SC', 'Hiragino Sans GB', 'Microsoft YaHei', sans-serif;
  --font-serif: 'Newsreader', 'Source Serif Pro', 'EB Garamond', Georgia, 'Times New Roman', serif;
  --font-mono: 'JetBrains Mono', ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;

  --maxw: 880px;
  --pad: clamp(1.25rem, 3.5vw, 2.5rem);
}

[data-theme="dark"] {
  --bg:          #0f1217;
  --bg-elev:    #161a21;
  --bg-soft:    #1b2029;
  --text:        #ebe7dc;
  --text-soft:  #b4b0a5;
  --text-mute:  #7d7a72;
  --rule:        #2a2f3a;
  --rule-soft:   #1f242d;
  --accent:      #c9a96a;
  --accent-soft: #d6b87a;
  --link:        #a9c4e8;
  --link-hover:  #d6e6ff;
  --badge-bg:    #20242d;
  --badge-fg:    #d6b87a;
  --pub-badge-bg: #1a2940;
  --pub-badge-fg: #93c5fd;
  --pub-highlight-bg: #3b82f6;
  --pub-highlight-fg: #ffffff;
  --shadow:      0 1px 2px rgba(0,0,0,.4), 0 8px 24px -16px rgba(0,0,0,.6);
}

/* -------------------------------- reset -------------------------------- */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.65;
  font-feature-settings: "ss01", "cv11", "kern";
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  transition: background-color .25s ease, color .25s ease;
}

img { max-width: 100%; display: block; }

/* -------------------------------- nav -------------------------------- */
.nav {
  position: sticky;
  top: 0;
  z-index: 30;
  background: color-mix(in oklab, var(--bg) 88%, transparent);
  -webkit-backdrop-filter: saturate(160%) blur(10px);
          backdrop-filter: saturate(160%) blur(10px);
  border-bottom: 1px solid var(--rule-soft);
}
.nav__inner {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: .85rem var(--pad);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}
.nav__brand {
  font-family: var(--font-serif);
  font-weight: 500;
  letter-spacing: .01em;
  color: var(--text);
  text-decoration: none;
  font-size: 1rem;
  white-space: nowrap;
  border-bottom: none;
}
.nav__brand:hover { border-bottom: none; color: var(--text); }
.nav__brand em { font-style: italic; color: var(--text-soft); font-weight: 400; }
@media (max-width: 720px) {
  .nav__brand em { display: none; }
}
.nav__links {
  display: flex;
  gap: 1.4rem;
  align-items: center;
}
.nav__links a {
  color: var(--text-soft);
  font-size: .89rem;
  text-decoration: none;
  letter-spacing: .015em;
  transition: color .15s ease;
}
.nav__links a:hover { color: var(--text); }
.theme-toggle {
  background: transparent;
  border: 1px solid var(--rule);
  color: var(--text-soft);
  width: 34px;
  height: 34px;
  border-radius: 999px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  transition: border-color .15s ease, color .15s ease, background-color .15s ease;
}
.theme-toggle:hover { color: var(--text); border-color: var(--accent-soft); }
.theme-toggle svg { width: 16px; height: 16px; }
[data-theme="dark"] .theme-toggle .icon-sun { display: inline; }
[data-theme="dark"] .theme-toggle .icon-moon { display: none; }
.theme-toggle .icon-sun { display: none; }
.theme-toggle .icon-moon { display: inline; }

@media (max-width: 640px) {
  .nav__links a { display: none; }
}

/* -------------------------------- layout -------------------------------- */
main {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 0 var(--pad) 5rem;
}

section { padding-top: 3.25rem; }
section + section { border-top: 1px solid var(--rule-soft); margin-top: 3.25rem; }
section h2 {
  font-family: var(--font-serif);
  font-weight: 500;
  font-size: 1.55rem;
  letter-spacing: -.005em;
  margin: 0 0 1.25rem;
  color: var(--text);
  display: flex;
  align-items: baseline;
  gap: .65rem;
}
section h2::before {
  content: '';
  display: inline-block;
  width: 24px;
  height: 1px;
  background: var(--accent);
  transform: translateY(-6px);
}

/* -------------------------------- hero -------------------------------- */
.hero {
  padding-top: 3.5rem;
  padding-bottom: 0;
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 2.25rem;
  align-items: center;
}
.hero__title {
  font-family: var(--font-serif);
  font-weight: 500;
  font-size: clamp(2rem, 5vw, 2.9rem);
  line-height: 1.1;
  letter-spacing: -.015em;
  margin: 0 0 .5rem;
}
.hero__title .zh {
  font-size: .55em;
  color: var(--text-soft);
  font-weight: 400;
  margin-left: .4em;
  letter-spacing: .02em;
}
.hero__role {
  color: var(--text-soft);
  font-size: 1.02rem;
  margin: 0 0 .25rem;
}
.hero__affil {
  color: var(--text-mute);
  font-size: .92rem;
  margin: 0 0 1.25rem;
}
.hero__links {
  display: flex;
  flex-wrap: wrap;
  gap: .5rem .65rem;
  align-items: center;
}
.hero__avatar {
  width: 132px;
  height: 132px;
  border-radius: 50%;
  overflow: hidden;
  box-shadow: var(--shadow);
  background: var(--bg-elev);
  border: 1px solid var(--rule);
}
.hero__avatar img, .hero__avatar svg { width: 100%; height: 100%; object-fit: cover; }

@media (max-width: 560px) {
  .hero { grid-template-columns: 1fr; gap: 1.5rem; }
  .hero__avatar { width: 104px; height: 104px; }
}

/* chips & links */
.chip {
  display: inline-flex;
  align-items: center;
  gap: .4rem;
  padding: .32rem .7rem;
  border: 1px solid var(--rule);
  border-radius: 999px;
  color: var(--text-soft);
  font-size: .82rem;
  text-decoration: none;
  background: var(--bg-elev);
  transition: border-color .15s ease, color .15s ease, transform .15s ease;
}
.chip:hover {
  color: var(--text);
  border-color: var(--accent-soft);
  border-bottom-color: var(--accent-soft);
  transform: translateY(-1px);
}
.chip svg { width: 14px; height: 14px; opacity: .85; }

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

/* -------------------------------- about -------------------------------- */
.lede {
  font-family: var(--font-serif);
  font-size: 1.18rem;
  line-height: 1.65;
  color: var(--text-soft);
  max-width: 64ch;
  margin: 0 0 1rem;
  letter-spacing: -.002em;
}
.about p { color: var(--text-soft); margin: 0 0 .9rem; }
.about p strong { color: var(--text); font-weight: 600; }

.interests {
  display: flex;
  flex-wrap: wrap;
  gap: .45rem;
  margin: 1rem 0 .25rem;
}
.tag {
  font-family: var(--font-mono);
  font-size: .76rem;
  letter-spacing: .02em;
  padding: .22rem .55rem;
  border-radius: 4px;
  background: var(--bg-soft);
  color: var(--text-soft);
  border: 1px solid var(--rule-soft);
}

/* -------------------------------- news -------------------------------- */
.news {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: .6rem;
}
.news li {
  display: grid;
  grid-template-columns: 110px 1fr;
  gap: 1.1rem;
  align-items: baseline;
  font-size: .96rem;
  color: var(--text-soft);
  padding: .15rem 0;
}
.news time {
  font-family: var(--font-mono);
  font-size: .76rem;
  letter-spacing: .04em;
  color: var(--text-mute);
  text-transform: uppercase;
}
.news .pin {
  display: inline-block;
  background: var(--accent);
  color: #fff;
  font-family: var(--font-mono);
  font-size: .68rem;
  letter-spacing: .08em;
  padding: .1rem .42rem;
  border-radius: 3px;
  margin-right: .35rem;
  vertical-align: 2px;
}
@media (max-width: 560px) {
  .news li { grid-template-columns: 1fr; gap: .15rem; }
}

/* -------------------------------- publications -------------------------------- */
.pub-controls {
  display: flex;
  flex-wrap: wrap;
  gap: .35rem;
  margin: 0 0 1.4rem;
}
.pub-tab {
  font: inherit;
  font-size: .82rem;
  padding: .35rem .8rem;
  background: transparent;
  border: 1px solid var(--rule);
  border-radius: 999px;
  color: var(--text-soft);
  cursor: pointer;
  transition: all .15s ease;
}
.pub-tab:hover { color: var(--text); border-color: var(--accent-soft); }
.pub-tab[aria-selected="true"] {
  background: var(--text);
  color: var(--bg);
  border-color: var(--text);
}

.pubs { list-style: none; padding: 0; margin: 0; }
.pubs li {
  display: grid;
  grid-template-columns: 7.5rem 1fr;
  gap: 1.25rem;
  padding: 1rem 0;
  border-top: 1px dashed var(--rule-soft);
}
.pubs li:first-child { border-top: 0; padding-top: 0; }

.pub-venue {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: .25rem;
  padding-top: .15rem;
}
.venue-badge {
  font-family: var(--font-mono);
  font-size: .7rem;
  letter-spacing: .04em;
  padding: .2rem .42rem;
  border-radius: 3px;
  background: var(--pub-badge-bg);
  color: var(--pub-badge-fg);
  font-weight: 600;
  white-space: nowrap;
}
.venue-badge.highlight {
  background: var(--pub-highlight-bg);
  color: var(--pub-highlight-fg);
}
.venue-year {
  font-family: var(--font-mono);
  font-size: .72rem;
  color: var(--text-mute);
  letter-spacing: .04em;
}

.pub-body .pub-title {
  font-weight: 600;
  color: var(--text);
  margin: 0 0 .2rem;
  line-height: 1.4;
  font-size: 1rem;
}
.pub-body .pub-authors {
  color: var(--text-soft);
  font-size: .9rem;
  margin: 0 0 .35rem;
}
.pub-body .pub-authors .me { color: var(--text); font-weight: 600; border-bottom: 1px solid var(--accent-soft); }
.pub-body .pub-meta {
  color: var(--text-mute);
  font-size: .84rem;
  font-style: italic;
  margin: 0 0 .35rem;
}
.pub-body .pub-links {
  display: flex;
  flex-wrap: wrap;
  gap: .35rem .55rem;
  font-size: .82rem;
}
.pub-body .pub-links a {
  color: var(--text-soft);
  border-bottom: 1px solid var(--rule);
  padding-bottom: 1px;
}
.pub-body .pub-links a:hover { color: var(--link); border-bottom-color: currentColor; }

.pubs li[hidden] { display: none; }

@media (max-width: 560px) {
  .pubs li { grid-template-columns: 1fr; gap: .55rem; }
  .pub-venue { flex-direction: row; align-items: center; gap: .5rem; }
}

/* -------------------------------- timeline (exp / edu) -------------------------------- */
.timeline { list-style: none; margin: 0; padding: 0; }
.timeline li {
  display: grid;
  grid-template-columns: 180px 1fr;
  gap: 1.25rem;
  padding: .75rem 0;
  border-top: 1px dashed var(--rule-soft);
}
.timeline li:first-child { border-top: 0; padding-top: 0; }
.timeline .when {
  font-family: var(--font-mono);
  font-size: .78rem;
  letter-spacing: .03em;
  color: var(--text-mute);
  padding-top: .15rem;
}
.timeline .what { font-size: .96rem; color: var(--text); }
.timeline .what .role { font-weight: 600; }
.timeline .what .org { color: var(--text-soft); }
.timeline .what .note { display: block; color: var(--text-mute); font-size: .86rem; margin-top: .15rem; }
@media (max-width: 560px) {
  .timeline li { grid-template-columns: 1fr; gap: .1rem; }
}

/* -------------------------------- service grid -------------------------------- */
.service-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 1rem 1.5rem;
}
.service-grid h3 {
  font-family: var(--font-sans);
  font-weight: 600;
  font-size: .82rem;
  letter-spacing: .08em;
  text-transform: uppercase;
  color: var(--text-mute);
  margin: 0 0 .55rem;
}
.service-grid ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  flex-wrap: wrap;
  gap: .35rem .45rem;
}
.service-grid li {
  font-family: var(--font-mono);
  font-size: .76rem;
  letter-spacing: .02em;
  padding: .22rem .55rem;
  border-radius: 4px;
  background: var(--bg-soft);
  color: var(--text-soft);
  border: 1px solid var(--rule-soft);
}

/* awards / projects list */
.simple-list { list-style: none; padding: 0; margin: 0; display: grid; gap: .5rem; }
.simple-list li {
  padding-left: 1rem;
  position: relative;
  color: var(--text-soft);
  font-size: .96rem;
}
.simple-list li::before {
  content: '';
  position: absolute;
  left: 0;
  top: .7em;
  width: 6px;
  height: 1px;
  background: var(--accent);
}

/* -------------------------------- footer -------------------------------- */
footer {
  max-width: var(--maxw);
  margin: 0 auto;
  padding: 2rem var(--pad) 3rem;
  border-top: 1px solid var(--rule-soft);
  color: var(--text-mute);
  font-size: .82rem;
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: .5rem;
}
footer a { color: var(--text-mute); }
footer a:hover { color: var(--text-soft); }

/* -------------------------------- print -------------------------------- */
@media print {
  .nav, .theme-toggle, .pub-controls { display: none; }
  body { background: white; color: black; }
  a { color: black; text-decoration: underline; }
}