:root{
  --bg:#0b0d12;
  --bg-soft:#111722;
  --panel:#151b26;
  --panel-2:#1c2533;
  --text:#eef4ff;
  --muted:#a8b4c7;
  --line:#344256;
  --green:#1db77f;
  --blue:#4f8cff;
  --orange:#f5a524;
  --red:#ef4b4b;
  --purple:#a77cff;
  --cyan:#22c8d8;
  --shadow:0 18px 48px rgba(0,0,0,.28);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  background:linear-gradient(180deg,#0b0d12 0%,#101723 44%,#0b0d12 100%);
  color:var(--text);
  font-family:Inter,ui-sans-serif,system-ui,-apple-system,Segoe UI,Roboto,Arial,sans-serif;
  line-height:1.55;
}
a{color:inherit;text-decoration:none}
p{color:#d3dbea;margin:8px 0}
h1,h2,h3{margin:0;color:#fff;letter-spacing:0}
h1{font-size:clamp(2.2rem,4.6vw,4.9rem);line-height:1.02}
h2{font-size:clamp(1.6rem,2.6vw,2.4rem);line-height:1.12}
h3{font-size:1.16rem;line-height:1.25}
.sr-only{
  position:absolute;
  width:1px;
  height:1px;
  padding:0;
  margin:-1px;
  overflow:hidden;
  clip:rect(0,0,0,0);
  white-space:nowrap;
  border:0;
}
.topbar{
  position:sticky;
  z-index:20;
  top:0;
  display:flex;
  align-items:center;
  justify-content:space-between;
  gap:18px;
  padding:14px clamp(18px,4vw,48px);
  background:rgba(11,13,18,.84);
  border-bottom:1px solid rgba(255,255,255,.07);
  backdrop-filter:blur(14px);
}
.brand{font-weight:850;font-size:1.05rem}
.main-nav{display:flex;gap:8px;flex-wrap:wrap;justify-content:flex-end}
.main-nav a,.button,.tab-list button,.step-controls button{
  border:1px solid rgba(255,255,255,.1);
  background:rgba(255,255,255,.045);
  color:#f8fbff;
  border-radius:8px;
  padding:8px 12px;
  font:700 .9rem/1 Inter,system-ui,sans-serif;
  cursor:pointer;
}
.main-nav a:hover,.main-nav a.active,.button.primary,.tab-list button.active,.step-controls button:hover{
  background:var(--green);
  border-color:var(--green);
  color:#07110d;
}
main{width:min(1180px,calc(100% - 36px));margin:0 auto}
.hero{
  min-height:calc(100vh - 72px);
  display:grid;
  grid-template-columns:minmax(0,1.05fr) minmax(320px,.78fr);
  gap:34px;
  align-items:center;
  padding:56px 0;
}
.hero p{max-width:760px;font-size:1.08rem;color:#c7d3e6}
.hero-actions{display:flex;gap:10px;flex-wrap:wrap;margin-top:22px}
.button{display:inline-flex;align-items:center;justify-content:center;min-height:40px}
.hero-panel{
  border:1px solid rgba(255,255,255,.09);
  background:linear-gradient(180deg,rgba(255,255,255,.05),rgba(255,255,255,.025)),var(--panel);
  border-radius:14px;
  padding:18px;
  box-shadow:var(--shadow);
}
.network-preview{
  position:relative;
  aspect-ratio:3/2;
  border-radius:10px;
  overflow:hidden;
  background:radial-gradient(circle at 22% 24%,rgba(79,140,255,.24),transparent 28%),radial-gradient(circle at 72% 70%,rgba(29,183,127,.22),transparent 28%),#0f1520;
}
.network-preview svg{position:absolute;inset:0;width:100%;height:100%}
.network-preview path{fill:none;stroke:#5e718d;stroke-width:4;stroke-linecap:round}
.network-preview span{
  position:absolute;
  left:var(--x);
  top:var(--y);
  z-index:2;
  display:grid;
  place-items:center;
  width:36px;
  height:36px;
  transform:translate(-50%,-50%);
  border-radius:50%;
  background:#172238;
  border:2px solid #b7c7e6;
  font-weight:850;
}
.mini-stats{display:grid;grid-template-columns:repeat(3,1fr);gap:10px;margin-top:12px}
.stat{border:1px solid rgba(255,255,255,.08);background:var(--panel-2);border-radius:8px;padding:12px}
.stat strong{display:block;font-size:1.55rem}
.stat span{font-size:.82rem;color:var(--muted)}
.section-shell{padding:22px 0 48px}
.section-shell.compact{padding-top:0}
.section-heading{display:flex;justify-content:space-between;gap:20px;align-items:end;margin-bottom:18px}
.section-heading p{max-width:620px;color:var(--muted)}
.section-heading.tight{align-items:start;display:block}
.topic-grid,.animation-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px}
.topic-card,.animation-card,.content-card,.exercise-card{
  border:1px solid rgba(255,255,255,.08);
  background:linear-gradient(180deg,rgba(255,255,255,.04),rgba(255,255,255,.015)),var(--panel);
  border-radius:10px;
  padding:16px;
  box-shadow:0 12px 32px rgba(0,0,0,.18);
}
.topic-card small,.source,.tag{color:#b9c8df;font-size:.82rem}
.tag{
  display:inline-flex;
  align-items:center;
  border:1px solid rgba(255,255,255,.1);
  border-radius:7px;
  padding:2px 7px;
  background:rgba(255,255,255,.045);
  margin:2px 4px 2px 0;
}
.app-layout{
  display:grid;
  grid-template-columns:300px minmax(0,1fr);
  gap:22px;
  align-items:start;
  width:min(1480px,calc(100% - 28px));
  padding:24px 0 54px;
  transition:grid-template-columns .2s ease;
}
.app-layout.rail-collapsed{
  grid-template-columns:58px minmax(0,1fr);
}
.rail{
  position:sticky;
  top:72px;
  max-height:calc(100vh - 92px);
  overflow:auto;
  border:1px solid rgba(255,255,255,.08);
  background:rgba(18,24,34,.9);
  border-radius:12px;
  padding:16px;
  transition:padding .2s ease,background .2s ease;
}
.rail h1{font-size:1.6rem}
.rail p{font-size:.92rem;color:var(--muted)}
.rail-head{display:flex;align-items:center;justify-content:space-between;gap:12px}
.rail-toggle{
  flex:0 0 auto;
  display:grid;
  place-items:center;
  width:34px;
  height:34px;
  border:1px solid rgba(255,255,255,.13);
  border-radius:8px;
  background:rgba(255,255,255,.055);
  cursor:pointer;
}
.rail-toggle:hover{border-color:var(--green);background:rgba(29,183,127,.16)}
.rail-toggle-lines,.rail-toggle-lines::before,.rail-toggle-lines::after{
  display:block;
  width:16px;
  height:2px;
  border-radius:3px;
  background:#e9f3ff;
}
.rail-toggle-lines{position:relative}
.rail-toggle-lines::before,.rail-toggle-lines::after{content:"";position:absolute;left:0}
.rail-toggle-lines::before{top:-6px}
.rail-toggle-lines::after{top:6px}
.rail-content{transition:opacity .15s ease,transform .15s ease}
.rail.is-collapsed{
  padding:12px 8px;
  overflow:hidden;
}
.rail.is-collapsed .rail-head{justify-content:center}
.rail.is-collapsed .rail-title,.rail.is-collapsed .rail-content{
  width:0;
  height:0;
  opacity:0;
  overflow:hidden;
  pointer-events:none;
  transform:translateX(-8px);
}
.tab-list{display:flex;flex-direction:column;gap:7px;margin-top:14px}
.tab-list button{text-align:left;line-height:1.2;color:#d8e3f5}
.tab-list button.active{color:#07110d}
.content-stage{min-width:0}
.content-card{margin-bottom:16px}
.content-card h2{margin-bottom:4px}
.content-card h3{margin-top:18px}
.content-card ul,.content-card ol{color:#d7dfec;padding-left:20px}
.content-card li{margin:6px 0}
.formula{
  overflow:auto;
  border:1px solid rgba(255,255,255,.08);
  border-radius:8px;
  background:#090e18;
  color:#dff6ff;
  padding:10px 12px;
  font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
}
.visual-grid{display:grid;gap:14px;margin-top:16px}
.visual-card{border:1px solid rgba(255,255,255,.08);border-radius:10px;background:#101620;padding:12px}
.graph-box{
  min-height:320px;
  display:grid;
  place-items:center;
  border:1px solid rgba(255,255,255,.07);
  border-radius:8px;
  background:#0b1220;
  overflow:hidden;
}
.graph-box svg{
  display:block;
  width:100%;
  max-width:100%;
  height:auto;
  max-height:min(62vh,540px);
  min-height:260px;
  aspect-ratio:var(--graph-ratio,720 / 380);
}
.step-controls{display:flex;align-items:center;gap:8px;margin-top:10px}
.step-controls span{flex:1;text-align:center;color:var(--muted);font-size:.9rem}
.step-text{margin-top:10px;border-left:3px solid var(--orange);padding-left:10px;color:#dce7f7}
.exercise-list{display:grid;gap:16px}
.exercise-card{padding:0;overflow:hidden}
.exercise-head{display:flex;justify-content:space-between;gap:12px;align-items:start;padding:16px;border-bottom:1px solid rgba(255,255,255,.08)}
.exercise-body{display:block;padding:16px}
.solution-toggle{margin-top:16px}
.prompt{white-space:pre-line;color:#e1e8f5}
.question-list{margin:10px 0 0;padding-left:20px;color:#dce5f4}
.solution{border-top:1px solid rgba(255,255,255,.08);padding:16px;background:rgba(255,255,255,.025)}
.solution ol{padding-left:20px;color:#dce5f4}
.solution-graph{margin-top:14px}
.solution-graph h4{margin:0 0 10px;color:#fff;font-size:1rem}
.prompt-graph-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(260px,1fr));gap:12px;margin-top:14px}
.prompt-graph-grid .solution-graph{margin-top:0}
.prompt-graph-grid .graph-box{min-height:260px}
.matrix-wrap{margin-top:16px;overflow:auto}
.matrix-wrap h3{margin-bottom:8px}
.matrix-table{
  min-width:max-content;
  border-collapse:collapse;
  border:1px solid rgba(255,255,255,.1);
  background:#09101c;
  font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
  font-size:.88rem;
}
.matrix-table th,.matrix-table td{
  min-width:38px;
  padding:7px 9px;
  border:1px solid rgba(255,255,255,.09);
  text-align:center;
  color:#dce8f8;
}
.matrix-table th{background:#111b2b;color:#fff}
.matrix-table tbody th{color:#b9cdf0}
.footer{width:min(1180px,calc(100% - 36px));margin:0 auto;padding:28px 0 42px;color:var(--muted)}
.svg-label{font-family:Inter,Arial,sans-serif;font-size:12px;font-weight:800;fill:#eaf2ff}
.svg-muted{fill:#b6c3d8}
@media (max-width:920px){
  .hero,.app-layout,.exercise-body{grid-template-columns:1fr}
  .hero{min-height:auto}
  .rail{position:relative;top:0;max-height:none}
  .app-layout.rail-collapsed{grid-template-columns:1fr}
  .rail.is-collapsed{padding:10px 12px}
  .rail.is-collapsed .rail-head{justify-content:space-between}
  .rail.is-collapsed .rail-title{
    width:auto;
    height:auto;
    opacity:1;
    transform:none;
  }
  .topic-grid,.animation-grid,.mini-stats{grid-template-columns:1fr}
  .section-heading{display:block}
  .topbar{position:relative;align-items:flex-start}
  .visual-card,.content-card,.graph-box{min-width:0}
  .graph-box svg{min-width:0;min-height:260px}
}
@media (prefers-reduced-motion:no-preference){
  .topic-card,.animation-card,.content-card,.exercise-card{transition:transform .18s ease,border-color .18s ease}
  .topic-card:hover,.animation-card:hover,.exercise-card:hover{transform:translateY(-2px);border-color:rgba(255,255,255,.18)}
}