:root{
  --primary:#1f4e79;
  --primary-dark:#163955;
  --accent:#6fa8dc;
  --bg:#f6f8fb;
  --card:#ffffff;
  --text:#1f2937;
  --muted:#6b7280;
  --line:#d9e2ec;
  --max:1100px;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  font-family:"Microsoft YaHei","PingFang SC","Noto Sans SC",Arial,sans-serif;
  color:var(--text);
  background:var(--bg);
  line-height:1.8;
}
a{color:var(--primary);text-decoration:none}
a:hover{text-decoration:underline}
.container{width:min(var(--max),92%);margin:0 auto}

/* --- Language Toggle --- */
.lang{display:none !important}
html[lang="zh-CN"] .lang.zh-cn{display:inline !important}
html[lang="zh-TW"] .lang.zh-tw{display:inline !important}
html[lang="en"]    .lang.en{display:inline !important}
html[lang="zh-CN"] div.lang.zh-cn,
html[lang="zh-CN"] p.lang.zh-cn,
html[lang="zh-CN"] ul.lang.zh-cn,
html[lang="zh-CN"] ol.lang.zh-cn,
html[lang="zh-CN"] li.lang.zh-cn,
html[lang="zh-CN"] section.lang.zh-cn,
html[lang="zh-CN"] h1.lang.zh-cn,
html[lang="zh-CN"] h2.lang.zh-cn,
html[lang="zh-CN"] h3.lang.zh-cn{display:block !important}
html[lang="zh-TW"] div.lang.zh-tw,
html[lang="zh-TW"] p.lang.zh-tw,
html[lang="zh-TW"] ul.lang.zh-tw,
html[lang="zh-TW"] ol.lang.zh-tw,
html[lang="zh-TW"] li.lang.zh-tw,
html[lang="zh-TW"] section.lang.zh-tw,
html[lang="zh-TW"] h1.lang.zh-tw,
html[lang="zh-TW"] h2.lang.zh-tw,
html[lang="zh-TW"] h3.lang.zh-tw{display:block !important}
html[lang="en"] div.lang.en,
html[lang="en"] p.lang.en,
html[lang="en"] ul.lang.en,
html[lang="en"] ol.lang.en,
html[lang="en"] li.lang.en,
html[lang="en"] section.lang.en,
html[lang="en"] h1.lang.en,
html[lang="en"] h2.lang.en,
html[lang="en"] h3.lang.en{display:block !important}

.lang-toggle{display:flex;gap:6px;align-items:center;flex-shrink:0}
.lang-btn{
  background:transparent;border:1px solid var(--line);
  padding:4px 10px;border-radius:8px;cursor:pointer;
  font-size:.85rem;color:var(--muted);font-weight:600;
  transition:all .2s;
}
.lang-btn:hover{border-color:var(--accent);color:var(--primary)}
.lang-btn.active{
  background:var(--primary);border-color:var(--primary);color:#fff;
}

/* --- Header --- */
header.site-header{
  background:#fff;
  border-bottom:1px solid var(--line);
  position:sticky; top:0; z-index:10;
}
header.site-header .container{width:min(1280px,96%)}
.nav-wrap{
  display:flex;justify-content:space-between;align-items:center;
  gap:8px 16px;padding:14px 0;flex-wrap:nowrap;
}
.brand{font-weight:700;font-size:1.05rem;color:var(--primary-dark)}
.header-right{display:flex;align-items:center;gap:12px;flex-shrink:0;flex-wrap:nowrap}
nav ul{
  list-style:none;margin:0;padding:0;display:flex;gap:18px;flex-wrap:wrap;
}
nav a{
  color:var(--text);font-weight:600;padding:8px 10px;border-radius:10px;
}
nav a.active, nav a:hover{
  background:#eef4fa;color:var(--primary-dark);text-decoration:none;
}

/* --- Hero --- */
.hero{
  background:
    linear-gradient(rgba(20,40,70,0.6), rgba(20,40,70,0.6)),
    url("../images/banner.jpg") center/cover no-repeat;
  color:#fff;
  padding:64px 0 54px;
}
.hero-grid{
  display:grid;grid-template-columns:1.5fr 0.9fr;gap:36px;align-items:center;
}
.hero h1{font-size:2.4rem;line-height:1.25;margin:0 0 12px}
.hero .subtitle{font-size:1.08rem;opacity:.95;margin-bottom:18px}
.tag-list{display:flex;flex-wrap:wrap;gap:10px;margin:18px 0 0;padding:0;list-style:none}
.tag{
  background:rgba(255,255,255,.14);border:1px solid rgba(255,255,255,.22);
  padding:8px 12px;border-radius:999px;font-size:.96rem
}
.hero-card{
  background:rgba(255,255,255,.1);
  border:1px solid rgba(255,255,255,.18);
  border-radius:22px;padding:24px;backdrop-filter:blur(6px);
}
.photo-placeholder, .banner-placeholder{
  border:2px dashed rgba(255,255,255,.55);
  border-radius:18px;display:flex;align-items:center;justify-content:center;
  text-align:center;min-height:280px;padding:24px;color:#eef6ff;
  font-weight:600;
}

/* --- Page Banner --- */
.page-banner{
  background:
    linear-gradient(rgba(20,40,70,0.6), rgba(20,40,70,0.6)),
    url("../images/banner.jpg") center/cover no-repeat;
  color:#fff;
  padding:64px 0 54px;
}
.page-banner h1{margin:0;font-size:2rem}
.page-banner p{margin:10px 0 0;opacity:.95}

/* --- Main Content --- */
main{padding:34px 0 60px}
.section{
  background:var(--card);border:1px solid var(--line);border-radius:22px;
  padding:28px;box-shadow:0 8px 24px rgba(15,23,42,.04);margin-bottom:22px;
}
.section h2{
  margin-top:0;color:var(--primary-dark);font-size:1.45rem;
  border-left:5px solid var(--accent);padding-left:12px;
}
.section h3{color:var(--primary-dark);margin-top:26px}
.lead{font-size:1.04rem}

/* --- Research Figure --- */
.research-fig{
  margin:20px auto;border-radius:14px;overflow:hidden;
  border:1px solid var(--line);
  max-width:60%;
}
.research-fig img{width:100%;display:block}
.research-fig figcaption{
  padding:10px 14px;font-size:.9rem;color:var(--muted);
  background:#f8fbff;text-align:center;
}

/* --- Grid & Cards --- */
.grid-2{display:grid;grid-template-columns:1fr 1fr;gap:22px}
.card-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:18px}
.card{
  border:1px solid var(--line);border-radius:18px;padding:18px;background:#fff;
}

/* --- Lists --- */
.muted{color:var(--muted)}
.timeline-list, .pub-list, .student-list, .plain-list{
  margin:0;padding-left:22px;
}
.pub-list li, .timeline-list li, .student-list li{margin-bottom:12px}
.pub-list .pub-links{margin-top:4px}
.pub-list .pub-links a{
  display:inline-block;margin-right:8px;padding:2px 10px;
  border:1px solid var(--accent);border-radius:6px;font-size:.85rem;
  color:var(--primary);font-weight:600;transition:all .2s;
}
.pub-list .pub-links a:hover{
  background:var(--primary);color:#fff;border-color:var(--primary);
  text-decoration:none;
}

/* --- Contact KV --- */
.kv{
  display:grid;grid-template-columns:130px 1fr;gap:8px 18px;align-items:start;
}
.kv div:nth-child(odd){font-weight:700;color:var(--primary-dark)}

/* --- Footer --- */
footer{
  padding:28px 0 40px;color:var(--muted);text-align:center;font-size:.95rem;
}

/* --- Note (dev only) --- */
.note{
  font-size:.94rem;color:var(--muted);background:#f8fbff;border-left:4px solid var(--accent);
  padding:12px 14px;border-radius:10px;
}

/* --- Profile Image --- */
.profile-img{
  width:100%;
  border-radius:18px;
  object-fit:cover;
}

/* --- Back-to-top Button --- */
.back-to-top{
  position:fixed;right:28px;bottom:28px;z-index:50;
  width:54px;height:54px;border-radius:50%;
  background:var(--primary);color:#fff;border:none;cursor:pointer;
  display:flex;flex-direction:column;align-items:center;justify-content:center;
  gap:1px;
  box-shadow:0 6px 18px rgba(31,78,121,.32);
  opacity:0;visibility:hidden;transform:translateY(10px);
  transition:opacity .25s ease, visibility .25s ease, transform .25s ease, background-color .2s;
  font-family:inherit;
}
.back-to-top.visible{opacity:1;visibility:visible;transform:translateY(0)}
.back-to-top:hover{background:var(--primary-dark)}
.back-to-top svg{display:block}
.back-to-top-label{
  font-size:.62rem;font-weight:700;letter-spacing:.5px;line-height:1;
  margin-top:1px;
}
@media (max-width: 600px){
  .back-to-top{right:16px;bottom:16px;width:48px;height:48px}
  .back-to-top-label{font-size:.55rem}
}

/* --- Responsive --- */
@media (max-width: 900px){
  .hero-grid,.grid-2{grid-template-columns:1fr}
  .hero h1{font-size:2rem}
  .photo-placeholder{min-height:220px}
  .nav-wrap{flex-wrap:wrap}
  .brand{max-width:100%;white-space:normal}
  .header-right{width:100%;justify-content:space-between}
}
@media (max-width: 600px){
  nav ul{gap:10px}
  nav a{padding:6px 8px;font-size:.9rem}
  .kv{grid-template-columns:100px 1fr}
}