:root{
  --bg:#030712;
  --bg-soft:#081227;
  --card:rgba(255,255,255,.05);
  --card-strong:rgba(255,255,255,.08);
  --border:rgba(255,255,255,.10);
  --text:#f8fafc;
  --muted:#cbd5e1;
  --accent:#7dd3fc;
  --button:#0f172a;
  --button-text:#f8fafc;
  --shadow:0 16px 40px rgba(0,0,0,.22);
}

body.light{
  --bg:#f8fbff;
  --bg-soft:#eef5ff;
  --card:rgba(255,255,255,.84);
  --card-strong:rgba(255,255,255,.95);
  --border:#dbe4ef;
  --text:#0f172a;
  --muted:#475569;
  --accent:#0369a1;
  --button:#ffffff;
  --button-text:#0f172a;
  --shadow:0 16px 38px rgba(15,23,42,.08);
}

*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Arial,sans-serif;
  background:
    radial-gradient(circle at top, rgba(56,189,248,.12), transparent 34%),
    linear-gradient(180deg,var(--bg) 0%, var(--bg-soft) 48%, var(--bg) 100%);
  color:var(--text);
  line-height:1.55;
}
body.light{
  background:
    radial-gradient(circle at top, rgba(14,165,233,.10), transparent 34%),
    linear-gradient(180deg,var(--bg) 0%, var(--bg-soft) 58%, #f8fafc 100%);
}
a{color:inherit;text-decoration:none}
.container{max-width:1720px;margin:0 auto;padding:24px}
.card{
  border:1px solid var(--border);
  background:var(--card);
  border-radius:28px;
  box-shadow:var(--shadow);
  backdrop-filter:blur(18px);
}
.card-inner{padding:24px}
header.hero{padding:24px}
.brand-row{display:flex;gap:16px;justify-content:space-between;align-items:flex-start;flex-wrap:wrap}
.brand{display:flex;gap:16px;min-width:0}
.logo{
  width:48px;height:48px;border-radius:18px;
  display:grid;place-items:center;
  background:#7dd3fc;color:#0f172a;font-weight:800;
  box-shadow:0 10px 26px rgba(56,189,248,.24)
}
.kicker{
  font-size:12px;
  letter-spacing:.24em;
  text-transform:uppercase;
  color:var(--accent);
  font-weight:700;
  margin-bottom:4px;
}
h1,h2,h3{margin:0 0 10px}
h1{font-size:clamp(2rem,4vw,3.5rem);line-height:1.06}
h2{font-size:clamp(1.4rem,2.2vw,2.2rem)}
h3{font-size:clamp(1.05rem,1.8vw,1.35rem)}
p{margin:0}
.hero-subtitle,.muted{color:var(--muted)}
.controls{display:flex;gap:10px;flex-wrap:wrap}
.btn{
  display:inline-flex;align-items:center;gap:8px;
  border-radius:18px;
  border:1px solid var(--border);
  padding:10px 15px;
  background:transparent;
  color:var(--text);
  cursor:pointer;
  transition:transform .18s ease, background .18s ease, border-color .18s ease, box-shadow .18s ease;
}
.btn:hover{transform:translateY(-2px);background:var(--card-strong)}
.btn:active{transform:scale(.98)}
.btn.primary{
  background:var(--button);
  color:var(--button-text);
}
.grid-home{
  display:grid;
  grid-template-columns:repeat(2,minmax(0,1fr));
  gap:24px;
  margin-top:24px;
}
.subject-card .meta,
.subject-header .meta{
  display:flex;gap:8px;flex-wrap:wrap;margin-bottom:14px
}
.badge{
  border:1px solid var(--border);
  background:var(--card-strong);
  border-radius:999px;
  padding:4px 10px;
  font-size:12px;
  font-weight:600;
}
.subject-card .location,
.subject-header .location,
.source-row{
  display:flex;align-items:flex-start;gap:8px;
  color:var(--muted);font-size:14px;margin-top:12px
}
.subject-card .actions{margin-top:18px}
.main-grid{
  display:grid;
  grid-template-columns:300px minmax(0,1fr) 320px;
  gap:24px;
  margin-top:24px;
  align-items:start;
}
.sticky{position:sticky;top:24px}
.nav-list,.source-notes{display:flex;flex-direction:column;gap:12px}
.nav-list{margin-top:14px}
.nav-pill{
  display:block;
  width:100%;
  text-align:left;
  border:1px solid var(--border);
  background:var(--card);
  color:var(--text);
  border-radius:24px;
  padding:14px 18px;
  min-height:52px;
  cursor:pointer;
  transition:background .16s ease, transform .16s ease;
}
.nav-pill:hover{background:var(--card-strong);transform:translateY(-1px)}
.nav-pill{font-size:14px;line-height:1.4;white-space:normal;overflow-wrap:anywhere;word-break:normal}
.section{margin-bottom:24px}
.section .toggle{
  width:100%;border:none;background:none;color:inherit;padding:0;cursor:pointer;
  display:flex;justify-content:space-between;align-items:flex-start;gap:14px
}
.question{
  border:1px solid var(--border);
  background:var(--card);
  border-radius:22px;
  padding:18px;
  margin-top:14px
}
.question-head{display:flex;gap:12px;align-items:flex-start;margin-bottom:10px}
.qn{
  min-width:44px;text-align:center;border-radius:14px;padding:6px 8px;
  font-size:13px;font-weight:700;background:rgba(125,211,252,.14);color:#bae6fd;border:1px solid var(--border)
}
body.light .qn{background:#e0f2fe;color:#0c4a6e}
.question p{margin:0 0 10px;color:var(--muted)}
.math{
  overflow-x:auto;
  border:1px solid var(--border);
  background:rgba(2,6,23,.58);
  border-radius:18px;
  padding:14px 16px;
  margin-top:10px;
}
body.light .math{background:#fff}
.warning .card-title{display:flex;align-items:center;gap:8px}
.source-box{
  border:1px solid var(--border);
  border-radius:20px;
  padding:16px;
  background:var(--card);
}
.source-controls{gap:12px}
iframe.pdf-viewer{
  width:100%;
  height:calc(100vh - 170px);
  min-height:820px;
  border:0;
  border-radius:16px;
  background:#fff;
  margin-top:8px;
}
.small{font-size:14px;color:var(--muted)}
.space{display:grid;gap:12px}
.footer-note{padding:18px 24px;color:var(--muted);font-size:14px}
.top-gap{margin-top:24px}
.hidden{display:none!important}
.chevron{transition:transform .18s ease}
.closed .chevron{transform:rotate(-90deg)}
.home-intro{margin-top:24px}

.source-column .sticky{
  top:24px;
}
.floating-source{
  position:fixed;
  top:222px;
  right:max(24px, calc((100vw - 1720px) / 2 + 24px));
  width:320px;
  z-index:22;
}
.floating-source .source-panel-card{
  max-height:calc(100vh - 206px);
  overflow:auto;
}
.source-panel-card{min-width:0}
.source-column .card{
  overflow:hidden;
}
.source-column .card-inner{
  display:flex;
  flex-direction:column;
  gap:14px;
}
.content-column{min-width:0}
.pdf-drawer{
  position:fixed;
  top:12px;
  right:12px;
  bottom:12px;
  width:min(54vw, 980px);
  min-width:700px;
  z-index:60;
  border:1px solid var(--border);
  background:color-mix(in srgb, var(--bg) 78%, transparent);
  backdrop-filter:blur(18px);
  border-radius:24px;
  box-shadow:0 24px 60px rgba(0,0,0,.34);
  display:flex;
  flex-direction:column;
  overflow:hidden;
  transform:translateX(24px);
  opacity:0;
  pointer-events:none;
  transition:transform .22s ease, opacity .22s ease;
}
body.light .pdf-drawer{
  background:rgba(255,255,255,.92);
}
body.pdf-open .pdf-drawer{
  transform:translateX(0);
  opacity:1;
  pointer-events:auto;
}
.pdf-drawer-head{
  display:flex;
  align-items:flex-start;
  justify-content:space-between;
  gap:12px;
  padding:18px 18px 12px;
  border-bottom:1px solid var(--border);
}
.pdf-drawer-body{
  flex:1 1 auto;
  min-height:0;
  padding:12px;
}
.pdf-drawer-actions{
  display:flex;
  align-items:center;
  gap:10px;
  flex-wrap:wrap;
}
.pdf-lang-switch{
  display:flex;
  gap:8px;
}
.pdf-lang-btn{
  min-width:56px;
  justify-content:center;
}
.pdf-lang-btn.is-active{
  background:var(--card-strong);
  border-color:color-mix(in srgb, var(--accent) 45%, var(--border));
  box-shadow:0 0 0 1px color-mix(in srgb, var(--accent) 22%, transparent) inset;
}

.pdf-drawer-frame{
  width:100%;
  height:100%;
  border:0;
  border-radius:16px;
  background:#fff;
}
.pdf-drawer-backdrop{
  position:fixed;
  inset:0;
  background:rgba(2,6,23,.18);
  opacity:0;
  pointer-events:none;
  transition:opacity .22s ease;
  z-index:55;
}
body.pdf-open .pdf-drawer-backdrop{
  opacity:1;
  pointer-events:auto;
}
@media (max-width:1200px){
  .main-grid{grid-template-columns:250px minmax(0,1fr)}
  .source-column{grid-column:1 / -1}
  .source-column .sticky{position:static}
  .pdf-drawer{
    top:10px;
    right:10px;
    bottom:10px;
    width:min(74vw, 920px);
    min-width:0;
  }
}
@media (max-width:860px){
  .grid-home{grid-template-columns:1fr}
  .main-grid{grid-template-columns:1fr}
  .sticky{position:static}
  iframe.pdf-viewer{height:78vh;min-height:560px}
  .pdf-drawer{
    top:0;
    right:0;
    bottom:0;
    width:100vw;
    min-width:0;
    border-radius:0;
  }
  .pdf-drawer-body{padding:8px}
  .container{padding:16px}
  header.hero,.card-inner{padding:18px}
}


@media (max-width: 1400px){
  .container{padding:20px}
  .main-grid{grid-template-columns:280px minmax(0,1fr) 300px;}
  .floating-source{width:300px; right:20px; top:214px;}
}

@media (max-width: 1180px){
  .main-grid{grid-template-columns:280px minmax(0,1fr);}
  .source-column{display:none;}
}