/* Qiuwei Liu — Portfolio | AI Systems / ML Engineering */
:root{
  --bg:#FAF9F5;
  --bg-alt:#F0EEE9;
  --card:#FFFFFF;
  --text:#1F1E1D;
  --muted:#6B6965;
  --line:#E5E2DB;
  --accent:#D97757;
  --accent-soft:#FBE9E2;
  --radius:12px;
  --max:1120px;
  --nav-h:56px;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
@media (prefers-reduced-motion:reduce){
  html{scroll-behavior:auto}
  *,*::before,*::after{animation:none !important;transition:none !important}
}
body{
  margin:0;
  font-family:ui-sans-system,-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,"Noto Sans",sans-serif;
  color:var(--text);
  background:var(--bg);
  line-height:1.7;
  -webkit-font-smoothing:antialiased;
  font-size:16px;
}
a{color:var(--accent);text-decoration:none}
a:hover{text-decoration:underline}
a:focus-visible,button:focus-visible{outline:2px solid var(--accent);outline-offset:2px}
.container{max-width:var(--max);margin:0 auto;padding:0 24px}
.narrow{max-width:720px}
.skip-link{position:absolute;left:-9999px;top:8px;background:#fff;padding:8px 12px;border:1px solid var(--line);border-radius:8px;z-index:99}
.skip-link:focus{left:12px}

/* Nav */
.nav{position:sticky;top:0;z-index:20;background:rgba(250,249,245,.92);backdrop-filter:saturate(1.2) blur(8px);border-bottom:1px solid var(--line)}
.nav-inner{max-width:var(--max);margin:0 auto;padding:0 24px;height:var(--nav-h);display:flex;align-items:center;justify-content:space-between;gap:16px}
.nav-brand{font-weight:700;letter-spacing:.02em;color:var(--text);font-size:1.05rem}
.nav-menu{display:flex;align-items:center;gap:20px}
.nav-menu a{color:var(--text);font-size:.92rem}
.lang-switch{border:1px solid var(--line);background:var(--card);padding:6px 10px;border-radius:999px;font-size:.85rem;cursor:pointer}
.nav-toggle{display:none;flex-direction:column;gap:4px;background:transparent;border:1px solid var(--line);border-radius:8px;padding:8px;cursor:pointer}
.nav-toggle span{display:block;width:18px;height:2px;background:var(--text);border-radius:2px}

/* Hero */
.hero{padding:80px 0 64px;border-bottom:1px solid var(--line);background:linear-gradient(180deg,#FFFFFF 0%,#FAF9F5 100%)}
.hero-grid{display:grid;grid-template-columns:1.05fr .95fr;gap:40px;align-items:center}
.hero-status{display:inline-flex;align-items:center;gap:8px;font-size:.88rem;color:#065f46;background:#ecfdf5;border:1px solid #a7f3d0;padding:6px 10px;border-radius:999px}
.dot{width:8px;height:8px;border-radius:50%;background:#10b981;box-shadow:0 0 0 4px rgba(16,185,129,.15)}
.hero h1{font-size:52px;line-height:1.05;margin:16px 0 8px;letter-spacing:-.03em;font-weight:800}
.hero-title{font-size:22px;font-weight:650;color:var(--accent);margin:0 0 12px;letter-spacing:-.01em}
.hero-tagline{font-size:16px;max-width:600px;color:#2F2D2A;margin:0 0 10px;line-height:1.65}
.hero-tech{font-family:ui-monospace,SFMono-Regular,Menlo,monospace;font-size:13px;color:var(--muted);margin:0 0 20px}
.hero-actions{display:flex;gap:12px;flex-wrap:wrap}
.btn{display:inline-flex;align-items:center;justify-content:center;padding:11px 18px;border-radius:10px;font-size:.94rem;border:1px solid transparent;cursor:pointer;text-decoration:none;transition:transform .15s ease, box-shadow .15s ease}
.btn:hover{transform:translateY(-1px);text-decoration:none}
.btn-primary{background:var(--text);color:#fff;box-shadow:0 8px 20px rgba(15,23,42,.14)}
.btn-secondary{background:var(--card);border-color:var(--line);color:var(--text)}
.btn-ghost{background:transparent;border-color:var(--line);color:var(--text)}
.btn.small{padding:6px 10px;font-size:.84rem}
.hero-visual{overflow:hidden;border-radius:16px;border:1px solid var(--line);background:#F5F3EF;aspect-ratio:16/9}
.hero-visual img{width:100%;height:100%;object-fit:cover;display:block}

/* Sections */
.section{padding:64px 0;border-bottom:1px solid var(--line)}
.section-alt{background:var(--bg-alt)}
.section h2{font-size:28px;letter-spacing:-.015em;margin:0 0 10px;font-weight:750}
.section-intro{color:var(--muted);margin:0 0 22px;font-size:15px}

/* Reveal */
.reveal{opacity:0;transform:translateY(18px);transition:opacity .55s ease, transform .55s ease}
.reveal.visible{opacity:1;transform:none}
@media (prefers-reduced-motion:reduce){.reveal{opacity:1;transform:none;transition:none}}

/* Cards - What I Can Help With */
.card-grid{display:grid;gap:18px}
.card-grid.four{grid-template-columns:repeat(4,1fr)}
.card{background:var(--card);border:1px solid var(--line);border-radius:16px;padding:20px;transition:transform .15s ease, box-shadow .15s ease}
.card:hover{transform:translateY(-2px);box-shadow:0 12px 28px rgba(15,23,42,.07)}
.card-icon{width:36px;height:36px;border-radius:10px;background:var(--accent-soft);border:1px solid #F3D5C8;display:flex;align-items:center;justify-content:center;margin-bottom:12px;color:var(--accent)}
.card-icon svg{width:18px;height:18px}
.card h3{font-size:16px;margin:0 0 8px;font-weight:650}
.card p{margin:0;color:#3B3834;font-size:14px;line-height:1.6}

/* Skills hierarchy */
.skills-grid{display:grid;grid-template-columns:repeat(4,1fr);gap:18px}
.chips{display:flex;flex-wrap:wrap;gap:8px;margin-top:10px}
.chips span{padding:6px 10px;border-radius:999px;font-size:13px;border:1px solid var(--line);background:#fff;color:#1e293b}
.chips span.core{background:#2D2A26;color:#fff;border-color:#2D2A26;font-weight:600}
.chips span.secondary{color:var(--muted);background:#f8fafc}

/* Projects */
.project-card{display:grid;grid-template-columns:1fr 1fr;gap:0;background:var(--card);border:1px solid var(--line);border-radius:20px;overflow:hidden;margin:22px 0;transition:transform .15s ease, box-shadow .15s ease;align-items:stretch}
.project-card:hover{transform:translateY(-2px);box-shadow:0 20px 36px rgba(15,23,42,.10)}
.project-card.featured{border-color:#F3D5C8;box-shadow:0 10px 28px rgba(217,119,87,.08)}
.project-media{background:#F5F3EF;display:flex;align-items:stretch;justify-content:stretch;overflow:hidden;min-height:0}
.project-media.media-video{aspect-ratio:16/9;align-self:start;justify-content:center}
.project-media img{width:100%;height:100%;object-fit:cover;display:block;flex:1;min-width:0;min-height:0;transition:transform .25s ease}
.project-media.media-video img{object-fit:contain}
.project-card:hover .project-media img{transform:scale(1.015)}
@media (prefers-reduced-motion:reduce){.project-card:hover .project-media img{transform:none}}
.project-body{padding:24px;display:flex;flex-direction:column;gap:10px;background:var(--card)}
.project-kicker{font-size:12px;letter-spacing:.07em;text-transform:uppercase;color:var(--accent);font-weight:700;margin:0}
.project-body h3{margin:0;font-size:22px;font-weight:750;letter-spacing:-.01em}
.project-tech{font-family:ui-monospace,monospace;font-size:12px;color:var(--muted);margin:0}
.project-pipeline{font-family:ui-monospace,monospace;font-size:12px;color:#3B3834;margin:0}
.project-list{margin:0;padding-left:18px;font-size:14px;color:#334155}
.project-list li{margin:3px 0}
.project-metrics{display:flex;gap:12px;flex-wrap:wrap;margin:4px 0}
.metric{background:var(--accent-soft);border:1px solid #F3D5C8;padding:10px 14px;border-radius:10px;min-width:140px}
.metric strong{display:block;font-size:17px}
.metric span{font-size:12px;color:var(--muted)}
.metric-highlight{background:#2D2A26;color:#fff;border-radius:12px;padding:14px;display:flex;justify-content:space-between;align-items:center}
.metric-highlight strong{font-size:18px}
.metric-highlight em{font-style:normal;background:#D97757;color:#fff;padding:4px 8px;border-radius:999px;font-size:13px}
.metric-highlight small{color:#cbd5e1;font-size:12px}
.project-note{font-size:13px;color:var(--muted);margin:0}
.project-note.small{color:#64748b}
.project-actions{display:flex;gap:10px;flex-wrap:wrap;margin-top:6px}
.yolo-switcher{display:flex;flex-direction:column;width:100%;height:100%;min-height:0}
.yolo-switcher img{width:100%;height:100%;object-fit:cover;display:block;flex:1;min-width:0;min-height:0}
.switcher-tabs{display:flex;gap:6px;padding:8px;background:var(--bg-alt);border-top:1px solid var(--line);flex-shrink:0}
.switcher-tabs button{flex:1;padding:7px 8px;border:1px solid var(--line);background:#fff;border-radius:8px;font-size:13px;cursor:pointer}
.switcher-tabs button[aria-selected="true"]{background:#2D2A26;color:#fff;border-color:#2D2A26}

/* Research */
.research-card{padding:22px}
.research-metrics{display:grid;grid-template-columns:repeat(4,1fr);gap:12px;margin:14px 0}
.research-metrics div{background:var(--card);border:1px solid var(--line);border-radius:12px;padding:14px;text-align:center}
.research-metrics strong{display:block;font-size:17px}
.research-metrics span{font-size:12px;color:var(--muted)}
.research-compare,.research-note{font-size:13px;color:var(--muted)}

/* About two-column */
.about-grid{display:grid;grid-template-columns:1fr 1fr;gap:32px}
.about-grid h3{font-size:15px;margin:0 0 8px;font-weight:700}
.about-grid p{margin:0 0 8px;font-size:14px;color:#334155}

/* Contact */
.contact-grid{display:grid;gap:12px;margin-top:16px}
.contact-item{display:flex;align-items:center;gap:12px;background:var(--card);border:1px solid var(--line);border-radius:12px;padding:14px;flex-wrap:wrap}
.contact-item span{min-width:70px;font-size:13px;color:var(--muted)}
.contact-item code{background:var(--bg-alt);padding:5px 8px;border-radius:6px;font-size:14px}
.contact-sub{color:var(--muted);font-size:15px}

/* Footer */
.footer{padding:20px 0;color:var(--muted);font-size:13px;text-align:center}
.footer a{color:var(--muted)}
.footer a:hover{color:var(--text)}

/* Modal */
.modal{position:fixed;inset:0;display:none;align-items:center;justify-content:center;z-index:50}
.modal.open{display:flex}
.modal-backdrop{position:absolute;inset:0;background:rgba(15,23,42,.6);backdrop-filter:blur(4px)}
.modal-content{position:relative;background:#000;border-radius:12px;overflow:hidden;max-width:min(90vw,900px);max-height:90vh;box-shadow:0 20px 40px rgba(0,0,0,.3)}
.modal-content video{width:100%;height:auto;display:block;max-height:80vh}
.modal-close{position:absolute;top:8px;right:8px;background:rgba(0,0,0,.6);color:#fff;border:none;border-radius:999px;width:32px;height:32px;font-size:18px;cursor:pointer;display:flex;align-items:center;justify-content:center}

/* Responsive */
@media (max-width: 980px){
  .hero-grid{grid-template-columns:1fr;gap:20px}
  .hero-visual{order:-1;aspect-ratio:16/10}
  .card-grid.four{grid-template-columns:repeat(2,1fr)}
  .skills-grid{grid-template-columns:repeat(2,1fr)}
  .project-card{grid-template-columns:1fr}
  .about-grid{grid-template-columns:1fr}
}
@media (max-width: 640px){
  .nav-toggle{display:flex}
  .nav-menu{position:fixed;top:var(--nav-h);left:0;right:0;background:var(--bg);border-bottom:1px solid var(--line);flex-direction:column;align-items:flex-start;padding:12px 24px;gap:12px;transform:translateY(-110%);opacity:0;pointer-events:none;transition:transform .2s ease, opacity .2s ease}
  .nav-menu.open{transform:translateY(0);opacity:1;pointer-events:auto}
  .card-grid.four{grid-template-columns:1fr}
  .skills-grid{grid-template-columns:1fr}
  .hero{padding:48px 0 36px}
  .hero h1{font-size:40px}
  .hero-title{font-size:20px}
}

/* Systems overview */
.system-media{align-items:center;justify-content:center;background:#2D2A26;color:#fff;padding:32px}
.system-diagram{font:14px/1.9 ui-monospace,monospace;white-space:pre-wrap;overflow-wrap:anywhere;margin:0;max-width:100%}
.hero-systems{padding:12px;max-width:100%;font-size:16px}
.hero-systems p{margin:4px 0 18px;color:#e6b29f;font-size:13px}
.hero-systems p:last-child{margin-bottom:0}
@media(max-width:980px){.hero-visual{order:0;aspect-ratio:auto;min-height:220px}}

/* Compact supporting project; featured cards retain the main visual emphasis. */
.compact-project{display:flex;align-items:center;justify-content:space-between;gap:20px;margin:22px 0;padding:20px 24px}
.compact-project .project-kicker{margin:0 0 6px;color:var(--muted);font-size:11px}
.compact-project h3{font-size:18px;margin:0 0 6px}
.compact-project .btn{flex-shrink:0}
@media(max-width:640px){.compact-project{align-items:flex-start;flex-direction:column;gap:14px}}