/* ── RESET & VARIABLES ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
img { max-width: 100%; height: auto; display: block; }

:root {
  --text: #1e1e1e;
  --muted: #555;
  --subtle: #888;
  --border: #e0e0e0;
  --bg: #ffffff;
  --max: 1100px;
  --content: 760px;
  --pad: clamp(1.5rem, 5vw, 4rem);
  --heading: clamp(16px, 1.2vw + 10px, 21px); /* matches slogan size */
}

body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  color: var(--text);
  background: var(--bg);
  font-size: clamp(15px, 1.1vw + 9px, 18px);
  line-height: 1.65;
  font-weight: 400;
}

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

/* ── NAV ── */
nav {
  position: sticky;
  top: 0;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
  padding: 0 var(--pad);
  z-index: 100;
}
.nav-inner {
  max-width: var(--max);
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}
.nav-name {
  font-size: clamp(15px, 1.1vw + 9px, 18px);
  font-weight: 550;
  line-height: 1.3;
  white-space: nowrap;
}
.nav-links {
  display: flex;
  gap: clamp(1rem, 2vw, 2.25rem);
  list-style: none;
}
.nav-links a {
  font-size: clamp(13px, 0.8vw + 9px, 15px);
  color: var(--text);
}
.nav-hamburger {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  font-size: 22px;
  line-height: 1;
  color: var(--text);
  padding: 4px 6px;
  flex-shrink: 0;
}

/* ── PAGE CONTENT ── */
.page-wrap {
  max-width: 960px;
  margin: 0 auto;
  padding: clamp(2.5rem, 4vw, 4rem) var(--pad);
}

/* ── SECTION HEADER ── */
.section-header {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 1rem;
  margin-bottom: 2rem;
  flex-wrap: wrap;
}
.section-header .section-label { margin-bottom: 0; }

/* ── SECTION LABEL (Research / Teaching / Service / About Wen) ── */
.section-label {
  font-size: var(--heading);
  font-weight: 700;
  color: var(--text);
  margin-bottom: 2rem;
  line-height: 1.3;
}

/* ── SECTION TABS ── */
.section-tabs {
  display: flex;
  gap: 1.5rem;
  flex-wrap: wrap;
  align-items: center;
}
.section-tab {
  font-size: 13px;
  color: var(--muted);
  border: none;
  padding: 0;
  white-space: nowrap;
  text-decoration: underline;
  text-underline-offset: 3px;
  transition: color 0.12s;
}
.section-tab:hover { color: var(--text); text-decoration: underline; }

/* ── SUBSECTION LABEL (Under Review / Work in Progress / Proceedings) ── */
.subsection-label {
  font-size: var(--heading);
  font-weight: 500;
  color: var(--muted);
  margin-top: 3rem;
  margin-bottom: 0;
  padding-bottom: 0.6rem;
  border-bottom: 1px solid var(--border);
  scroll-margin-top: 84px; /* clears the 64px sticky nav + breathing room */
}

/* ── PAPERS ── */
.paper {
  padding: 1.5rem 0;
  border-bottom: 1px solid var(--border);
}
.paper-title {
  font-size: clamp(14px, 0.9vw + 9px, 16.5px);
  font-weight: 600;
  line-height: 1.45;
  margin-bottom: 0.3rem;
}
.paper-authors {
  font-size: clamp(13px, 0.7vw + 9px, 15px);
  color: var(--muted);
  margin-bottom: 0.2rem;
}
.paper-venue {
  font-size: clamp(12px, 0.6vw + 8px, 14px);
  color: var(--subtle);
  font-style: italic;
}
.paper-stage {
  font-size: 13px;
  color: var(--subtle);
  margin-top: 0.2rem;
}
.paper-awards {
  margin-top: 0.4rem;
  display: flex;
  flex-direction: column;
  gap: 0.15rem;
}
.award {
  font-size: 13px;
  color: var(--muted);
}
.paper-abstract {
  font-size: clamp(13px, 0.7vw + 9px, 15px);
  color: var(--muted);
  line-height: 1.75;
  margin-top: 0.75rem;
  display: none;
}
.paper-abstract.open { display: block; }
.paper-links {
  margin-top: 0.6rem;
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}
.paper-links a,
.toggle-abstract {
  font-family: inherit;
  font-size: 13px;
  color: var(--text);
  border: 1px solid #ccc;
  padding: 3px 12px;
  border-radius: 2px;
  background: none;
  cursor: pointer;
  line-height: 1.6;
  transition: background 0.12s;
  text-decoration: none;
}
.paper-links a:hover,
.toggle-abstract:hover { background: #f5f5f5; text-decoration: none; }

/* ── PLAIN LIST (teaching / service) ── */
.plain-list {
  list-style: none;
  font-size: clamp(14px, 0.9vw + 9px, 17px);
}
.plain-list li {
  padding: 0.85rem 0;
  border-bottom: 1px solid var(--border);
  line-height: 1.6;
}
.plain-list li:first-child { border-top: 1px solid var(--border); }
.plain-list .sub {
  font-size: clamp(12px, 0.7vw + 8px, 14.5px);
  color: var(--muted);
  display: block;
}

/* ── DIVIDER ── */
hr { border: none; border-top: 1px solid var(--border); }
hr[id] { scroll-margin-top: 84px; }

/* ── FOOTER ── */
footer {
  border-top: 1px solid var(--border);
  padding: clamp(3rem, 5vw, 5rem) var(--pad);
  text-align: center;
}
.footer-name {
  font-size: clamp(20px, 1.8vw + 10px, 28px);
  font-weight: 600;
  margin-bottom: 0.75rem;
}
.footer-info {
  font-size: clamp(13px, 0.8vw + 8px, 15.5px);
  color: var(--muted);
  line-height: 2;
}
.footer-info a { color: var(--muted); }
.footer-info a:hover { color: var(--text); text-decoration: underline; }

/* ── TEACHING PAGE ── */
.teaching-photo {
  width: 200px;
  height: 220px;
  object-fit: cover;
  object-position: center top;
  display: block;
  flex-shrink: 0;
  border-radius: 4px;
}
.course-with-photo {
  display: flex;
  gap: 1.5rem;
  align-items: flex-start;
}
.course-content { flex: 1; }
.paper-img {
  width: 220px;
  height: auto;
  object-fit: contain;
  display: block;
  flex-shrink: 0;
  border-radius: 4px;
}
.service-photo-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 6px;
  width: 220px;
  flex-shrink: 0;
  align-self: flex-start;
}
.service-photo-grid img {
  width: 100%;
  aspect-ratio: 1;
  object-fit: cover;
  border-radius: 3px;
  display: block;
}
.teaching-block { margin-top: 1.25rem; }
.teaching-institution {
  font-size: clamp(14px, 0.9vw + 9px, 16px);
  font-weight: 600;
  color: var(--text);
  margin-bottom: 0.75rem;
  padding-bottom: 0.4rem;
  border-bottom: 1px solid var(--border);
}
.course {
  padding: 0.75rem 0;
  border-bottom: 1px solid var(--border);
}
.course-header {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 1rem;
  margin-bottom: 0.25rem;
  flex-wrap: wrap;
}
.course-name {
  font-size: clamp(14px, 0.9vw + 9px, 16px);
  font-weight: 500;
  color: var(--text);
  flex: 1;
}
.course-term {
  font-size: 13px;
  color: var(--subtle);
  white-space: nowrap;
  flex-shrink: 0;
}
.course-meta {
  font-size: 13px;
  color: var(--muted);
  margin-bottom: 0.3rem;
}
.course-topics {
  font-size: 13px;
  color: var(--muted);
  line-height: 1.65;
}
.course-list {
  list-style: none;
}
.course-list li {
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  gap: 1rem;
  padding: 0.2rem 0;
  font-size: 13px;
  color: var(--muted);
  line-height: 1.65;
}
.course-list .course-name { font-weight: 400; font-size: inherit; color: inherit; }

/* ── ABOUT PAGE ── */
/*
  Layout (4 cols × 3 rows):
  [ 1 BIG  ][ 1 BIG  ][ 2  ][ 3  ]
  [ 1 BIG  ][ 1 BIG  ][ 4 WIDE   ]
  [ 5  ][ 6  ][ 7  ][ 8  ]
*/
.about-photos {
  display: flex;
  gap: 8px;
  align-items: flex-start;
  margin-bottom: 2.5rem;
}
.about-col {
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 8px;
}
.about-photos img {
  width: 100%;
  object-fit: cover;
  object-position: center;
  border-radius: 4px;
  display: block;
}

.about-text-block {
  margin-top: 1.25rem;
  margin-bottom: 0.5rem;
  display: flex;
  flex-direction: column;
  gap: 1.1rem;
}
.about-text-block p { text-align: justify; }

/* ── RESPONSIVE ── */
@media (max-width: 680px) {
  /* ── MOBILE NAV ── */
  .nav-inner {
    justify-content: space-between;
    gap: 0;
  }
  .nav-hamburger {
    display: flex;
    align-items: center;
    justify-content: center;
    margin-left: auto;
    padding: 8px;
  }
  .nav-links {
    display: none;
    position: fixed;
    top: 64px;
    left: 0;
    right: 0;
    flex-direction: column;
    background: var(--bg);
    border-bottom: 2px solid var(--border);
    box-shadow: 0 8px 24px rgba(0,0,0,0.10);
    z-index: 999;
    padding: 0;
    gap: 0;
    /* slide-down animation */
    animation: none;
  }
  .nav-links.open {
    display: flex;
    animation: navSlideDown 0.18s ease;
  }
  @keyframes navSlideDown {
    from { opacity: 0; transform: translateY(-8px); }
    to   { opacity: 1; transform: translateY(0); }
  }
  .nav-links li {
    border-bottom: 1px solid var(--border);
    flex-shrink: unset;
  }
  .nav-links li:last-child { border-bottom: none; }
  .nav-links a {
    display: block;
    padding: 1rem var(--pad);
    font-size: 16px;
    white-space: nowrap;
  }
  .section-header { flex-direction: column; gap: 0.75rem; }
  .page-wrap { padding-left: 1rem; padding-right: 1rem; }
  .course-list li { flex-wrap: wrap; gap: 0.1rem; }
  .course-header { flex-direction: column; gap: 0.1rem; }
  .course-with-photo { flex-direction: column; }
  .teaching-photo { width: 100%; height: 220px; }
  .paper-img { width: 100%; }
  .service-photo-grid { width: 100%; }
  .about-photos { flex-wrap: wrap; }
  .about-col { flex: 1 1 40%; }
}