/* ==========================================================================
   Wei You — single-page academic website
   Clean, minimal design inspired by the reference layout provided by user.
   ========================================================================== */

:root{
  --color-primary: #003366;
  --color-accent: #996600;
  --color-text: #1f2937;           /* slate-800 */
  --color-text-secondary: #475569; /* slate-600 */
  --color-text-muted: #64748b;     /* slate-500 */
  --color-bg: #ffffff;
  --color-bg-alt: #f8fafc;         /* slate-50 */
  --color-surface: #ffffff;
  --color-border: #e2e8f0;         /* slate-200 */
  --color-shadow: rgba(15, 23, 42, 0.08);

  --nav-bg: rgba(255,255,255,0.92);

  --font-en: "Inter", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
  --font-cn: "Noto Sans SC", "PingFang SC", "Microsoft YaHei", "Heiti SC", sans-serif;

  --radius: 12px;
  --radius-sm: 10px;
  --nav-height: 60px;

  --container: 980px;
}

/* Dark mode (optional) */
@media (prefers-color-scheme: dark){
  :root{
    --color-text: #e5e7eb;
    --color-text-secondary: #cbd5e1;
    --color-text-muted: #94a3b8;
    --color-bg: #0b1220;
    --color-bg-alt: #0f172a;
    --color-surface: #0b1220;
    --color-border: rgba(148, 163, 184, 0.18);
    --color-shadow: rgba(0, 0, 0, 0.35);
    --nav-bg: rgba(11,18,32,0.88);
  }
}

*{ box-sizing: border-box; }
html{ scroll-behavior: smooth; }
body{
  margin: 0;
  font-family: var(--font-en);
  color: var(--color-text);
  background:
    radial-gradient(1200px 600px at 20% -10%, rgba(0, 51, 102, 0.12), transparent 60%),
    radial-gradient(1000px 600px at 90% 10%, rgba(153, 102, 0, 0.10), transparent 55%),
    var(--color-bg);
  line-height: 1.7;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

a{
  color: inherit;
  text-decoration: none;
}
a:hover{ text-decoration: underline; }

img{ max-width: 100%; height: auto; }

.container{
  max-width: var(--container);
  margin: 0 auto;
  padding: 0 22px;
}

/* ==========================================================================
   Navigation
   ========================================================================== */

.nav{
  position: fixed;
  top: 0; left: 0; right: 0;
  height: var(--nav-height);
  z-index: 1000;
  background: var(--nav-bg);
  backdrop-filter: blur(14px);
  border-bottom: 1px solid var(--color-border);
}

.nav-inner{
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 14px;
}

.brand{
  font-weight: 600;
  letter-spacing: -0.01em;
  font-size: 1.06rem;
  color: var(--color-text);
  display: inline-flex;
  align-items: center;
  gap: 10px;
}

.brand-dot{
  width: 10px;
  height: 10px;
  border-radius: 999px;
  background: linear-gradient(135deg, var(--color-primary), var(--color-accent));
  display: inline-block;
}

.nav-links{
  list-style: none;
  display: flex;
  gap: 22px;
  padding: 0;
  margin: 0;
  align-items: center;
}

.nav-link{
  cursor: pointer;
  color: var(--color-text-muted);
  font-weight: 500;
  padding: 8px 0;
  text-decoration: none;
  transition: color 0.2s ease;
  position: relative;
}

.nav-link:hover{ color: var(--color-text); text-decoration: none; }

.nav-link.active{
  color: var(--color-text);
}

.nav-link.active::after{
  content: "";
  position: absolute;
  left: 0; right: 0;
  bottom: -10px;
  height: 2px;
  background: linear-gradient(90deg, var(--color-primary), var(--color-accent));
  border-radius: 2px;
}

.nav-toggle{
  display: none;
  border: 1px solid var(--color-border);
  background: transparent;
  color: var(--color-text);
  border-radius: 10px;
  padding: 8px 10px;
  cursor: pointer;
}

@media (max-width: 860px){
  .nav-toggle{ display: inline-flex; align-items: center; gap: 8px; }
  .nav-links{
    position: absolute;
    top: calc(var(--nav-height) + 10px);
    right: 16px;
    left: 16px;
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    padding: 10px;
    background: var(--color-surface);
    border: 1px solid var(--color-border);
    border-radius: var(--radius);
    box-shadow: 0 18px 60px var(--color-shadow);
    display: none;
  }
  .nav-links.open{ display: flex; }
  .nav-link{
    padding: 10px 12px;
    border-radius: 10px;
  }
  .nav-link.active::after{ display: none; }
  .nav-link.active{
    background: var(--color-bg-alt);
  }
}

/* ==========================================================================
   Pages
   ========================================================================== */

.page{
  display: none;
  min-height: 100vh;
  padding-top: var(--nav-height);
}

.page.active{ display: block; }

.page-content{
  padding: 54px 0 72px;
}

.page-title{
  font-size: 1.75rem;
  font-weight: 650;
  letter-spacing: -0.02em;
  margin: 0 0 20px;
}

.page-subtitle{
  color: var(--color-text-secondary);
  margin-top: -8px;
  margin-bottom: 26px;
}

/* Motion */
@media (prefers-reduced-motion: no-preference){
  .fade-in{ animation: fadeIn 260ms ease-out; }
}
@keyframes fadeIn{
  from{ opacity: 0; transform: translateY(6px); }
  to{ opacity: 1; transform: translateY(0); }
}

/* ==========================================================================
   Home
   ========================================================================== */

.hero{
  display: grid;
  grid-template-columns: 160px 1fr;
  gap: 22px;
  align-items: center;
  padding: 26px;
  border-radius: calc(var(--radius) + 6px);
  border: 1px solid var(--color-border);
  background: rgba(255,255,255,0.88);
  box-shadow: 0 10px 30px var(--color-shadow);
}

@media (prefers-color-scheme: dark){
  .hero{ background: rgba(11,18,32,0.88); }
}

.avatar{
  width: 140px;
  height: 140px;
  border-radius: 999px;
  overflow: hidden;
  border: 1px solid var(--color-border);
  background: var(--color-bg-alt);
  display: grid;
  place-items: center;
}

.avatar img{
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.hero h1{
  margin: 0;
  font-size: 2.2rem;
  line-height: 1.15;
  letter-spacing: -0.03em;
}

.name-cn{
  font-family: var(--font-cn);
  font-weight: 400;
  color: var(--color-text-secondary);
  margin-left: 10px;
  font-size: 1.25rem;
}

.hero-title{
  margin: 10px 0 14px;
  color: var(--color-text-secondary);
  line-height: 1.55;
}

.hero-links{
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
}

.pill{
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 8px 12px;
  border-radius: 999px;
  border: 1px solid var(--color-border);
  background: rgba(255,255,255,0.72);
  color: var(--color-text-secondary);
  font-weight: 520;
  transition: transform 0.15s ease, border-color 0.15s ease, color 0.15s ease;
}

@media (prefers-color-scheme: dark){
  .pill{ background: rgba(11,18,32,0.72); }
}

.pill:hover{
  text-decoration: none;
  transform: translateY(-1px);
  border-color: rgba(100,116,139,0.55);
  color: var(--color-text);
}

.pill svg{
  width: 18px;
  height: 18px;
}

.home-grid{
  display: grid;
  grid-template-columns: 1.25fr 0.75fr;
  gap: 18px;
  margin-top: 18px;
}

@media (max-width: 860px){
  .hero{ grid-template-columns: 1fr; text-align: center; }
  .avatar{ margin: 0 auto; }
  .hero-links{ justify-content: center; }
  .home-grid{ grid-template-columns: 1fr; }
}

.card{
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: var(--color-surface);
  padding: 18px 18px 16px;
  box-shadow: 0 8px 24px var(--color-shadow);
}

.card h2{
  margin: 0 0 12px;
  font-size: 1.05rem;
  font-weight: 650;
  letter-spacing: -0.01em;
}

.muted{ color: var(--color-text-secondary); }

.tags{
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.tag{
  font-size: 0.9rem;
  padding: 6px 10px;
  border-radius: 999px;
  border: 1px solid var(--color-border);
  background: var(--color-bg-alt);
}

/* ==========================================================================
   Research
   ========================================================================== */

.controls{
  display: flex;
  flex-wrap: wrap;
  gap: 12px;
  align-items: center;
  justify-content: space-between;
  border: 1px solid var(--color-border);
  background: rgba(255,255,255,0.84);
  border-radius: var(--radius);
  padding: 12px;
  margin: 14px 0 22px;
}

@media (prefers-color-scheme: dark){
  .controls{ background: rgba(11,18,32,0.84); }
}

.filters{
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
}

.filter-btn{
  border: 1px solid var(--color-border);
  background: transparent;
  color: var(--color-text-muted);
  padding: 7px 12px;
  border-radius: 999px;
  cursor: pointer;
  font-weight: 550;
  transition: border-color 0.15s ease, color 0.15s ease, background 0.15s ease;
}

.filter-btn:hover{
  border-color: rgba(100,116,139,0.55);
  color: var(--color-text);
}

.filter-btn.active{
  background: linear-gradient(135deg, rgba(0,51,102,0.14), rgba(153,102,0,0.14));
  border-color: rgba(0,51,102,0.35);
  color: var(--color-text);
}

.search{
  flex: 1;
  min-width: 220px;
  display: flex;
  justify-content: flex-end;
}

.search input{
  width: min(420px, 100%);
  padding: 9px 12px;
  border-radius: 999px;
  border: 1px solid var(--color-border);
  background: var(--color-bg);
  color: var(--color-text);
  outline: none;
}

.search input:focus{
  border-color: rgba(0,51,102,0.55);
  box-shadow: 0 0 0 4px rgba(0,51,102,0.18);
}

.section-title{
  margin: 30px 0 12px;
  font-size: 1.25rem;
  font-weight: 650;
  letter-spacing: -0.01em;
}

.paper-list{
  display: grid;
  grid-template-columns: 1fr;
  gap: 12px;
}

.paper{
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: var(--color-surface);
  padding: 14px 14px 12px;
  box-shadow: 0 8px 20px var(--color-shadow);
}

.paper-header{
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 12px;
}

.paper-year{
  font-variant-numeric: tabular-nums;
  font-weight: 650;
  color: var(--color-text-muted);
  font-size: 0.95rem;
}

.badge{
  font-size: 0.72rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  padding: 4px 10px;
  border-radius: 999px;
  border: 1px solid var(--color-border);
  color: var(--color-text-secondary);
  background: var(--color-bg-alt);
}

.badge.working{ border-color: rgba(153,102,0,0.55); }
.badge.journal{ border-color: rgba(0,51,102,0.55); }
.badge.conference{ border-color: rgba(14,165,233,0.55); }
.badge.thesis{ border-color: rgba(139,92,246,0.55); }

.paper-title{
  margin: 8px 0 6px;
  font-size: 1.05rem;
  font-weight: 650;
  line-height: 1.35;
}

.paper-meta{
  margin: 0;
  color: var(--color-text-secondary);
  font-size: 0.95rem;
}

.paper-venue{
  margin: 6px 0 0;
  color: var(--color-text-secondary);
  font-size: 0.95rem;
}

.paper-links{
  margin-top: 10px;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.paper-links a{
  font-size: 0.9rem;
  font-weight: 600;
  color: var(--color-primary);
  text-decoration: none;
}

.paper-links a:hover{ text-decoration: underline; }

.hidden{ display: none !important; }

/* ==========================================================================
   Lists / text blocks
   ========================================================================== */

.prose p{ margin: 0 0 12px; }
.prose p:last-child{ margin-bottom: 0; }

.simple-list{
  margin: 0;
  padding-left: 18px;
}

.timeline{
  display: grid;
  gap: 10px;
}

.timeline-item{
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: var(--color-surface);
  padding: 12px 14px;
  box-shadow: 0 8px 18px var(--color-shadow);
}

.timeline-item .t-year{
  color: var(--color-text-muted);
  font-weight: 650;
  font-variant-numeric: tabular-nums;
}

.timeline-item .t-title{
  margin-top: 2px;
  font-weight: 650;
}

.timeline-item .t-details{
  color: var(--color-text-secondary);
  margin-top: 6px;
}

/* Talks */
.talks-grid{
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 18px;
}

@media (max-width: 860px){
  .talks-grid{ grid-template-columns: 1fr; }
}

.talks-card ul{ margin: 0; padding-left: 18px; }
.talks-card li{ margin: 8px 0; color: var(--color-text-secondary); }
.talks-card em{ color: var(--color-text); font-style: normal; font-weight: 650; }

/* Students */
.student-grid{
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 12px;
}

.student-card{
  border: 1px solid var(--color-border);
  border-radius: var(--radius);
  background: var(--color-surface);
  padding: 12px 14px;
  box-shadow: 0 8px 18px var(--color-shadow);
}

.student-card .student-name{
  font-weight: 650;
}

.student-card .student-note{
  color: var(--color-text-secondary);
  margin-top: 4px;
  font-size: 0.95rem;
}

/* Footer */
.footer{
  border-top: 1px solid var(--color-border);
  padding: 20px 0 28px;
  color: var(--color-text-muted);
  font-size: 0.9rem;
}