:root{
  --bg:#0b0d12;
  --bg-soft:#101825;
  --panel:#151b25;
  --panel-2:#1b2635;
  --text:#eef5ff;
  --muted:#aab8cb;
  --line:#334255;
  --blue:#4f8cff;
  --green:#19b77c;
  --amber:#f5a524;
  --red:#ef5656;
  --purple:#a77cff;
  --cyan:#28c7d8;
  --shadow:0 18px 46px rgba(0,0,0,.26);
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{
  margin:0;
  background:linear-gradient(180deg,#0b0d12 0%,#101725 48%,#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:#d5deec;margin:8px 0}
h1,h2,h3,h4{margin:0;color:#fff;letter-spacing:0}
h1{font-size:clamp(2.15rem,4.4vw,4.75rem);line-height:1.02}
h2{font-size:clamp(1.55rem,2.5vw,2.35rem);line-height:1.12}
h3{font-size:1.14rem;line-height:1.25}
h4{font-size:1rem;line-height:1.25;margin-top:16px}
.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,.85);
  border-bottom:1px solid rgba(255,255,255,.07);
  backdrop-filter:blur(14px);
}
.brand{font-weight:850;font-size:1.08rem}
.main-nav{display:flex;gap:8px;flex-wrap:wrap;justify-content:flex-end}
.main-nav a,.button,.tab-list button,.step-controls button,.tool-form button,.solution-toggle{
  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,.tool-form button,.solution-toggle: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:780px;font-size:1.08rem;color:#c8d5e8}
.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 20% 28%,rgba(79,140,255,.22),transparent 28%),
    radial-gradient(circle at 74% 72%,rgba(25,183,124,.2),transparent 28%),
    #0f1520;
}
.network-preview svg{position:absolute;inset:0;width:100%;height:100%}
.network-preview path{fill:none;stroke:#6c809b;stroke-width:5;stroke-linecap:round}
.network-preview span{
  position:absolute;
  left:var(--x);
  top:var(--y);
  z-index:2;
  display:grid;
  place-items:center;
  min-width:42px;
  height:36px;
  padding:0 8px;
  transform:translate(-50%,-50%);
  border-radius:999px;
  background:#172238;
  border:2px solid #b7c7e6;
  font-size:.76rem;
  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:640px;color:var(--muted)}
.section-heading.tight{display:block;align-items:start}
.topic-grid,.material-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px}
.topic-card,.material-card,.content-card,.exercise-card,.tool-card,.visual-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,.material-card small,.source,.tag{color:#bbcae1;font-size:.82rem}
.source{display:inline-block;max-width:100%;overflow-wrap:anywhere;word-break:break-word}
.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:304px 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,.92);
  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(25,183,124,.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:4px 0 8px}
.content-card h3{margin-top:18px}
.content-card ul,.content-card ol{color:#d7dfec;padding-left:20px}
.content-card li{margin:6px 0}
.diagram-panel{
  margin-top:16px;
  border:1px solid rgba(255,255,255,.08);
  border-radius:10px;
  background:#0b1220;
  padding:14px;
}
.diagram-flow{
  display:flex;
  align-items:center;
  gap:10px;
  flex-wrap:wrap;
}
.diagram-node{
  border:1px solid rgba(255,255,255,.12);
  background:#172238;
  border-radius:8px;
  padding:10px 12px;
  color:#eef5ff;
  font-weight:800;
}
.diagram-arrow{color:var(--amber);font-weight:900}
.command-block,.formula{
  overflow:auto;
  border:1px solid rgba(255,255,255,.08);
  border-radius:8px;
  background:#080e18;
  color:#dff6ff;
  padding:10px 12px;
  font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
  white-space:pre-wrap;
}
.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}
.prompt{white-space:pre-line;color:#e1e8f5}
.table-block{margin-top:14px}
.table-block h4{margin:0 0 8px;font-size:.92rem;color:#f8fbff}
.table-scroll{
  max-width:100%;
  overflow-x:auto;
  border:1px solid rgba(255,255,255,.1);
  border-radius:8px;
  background:rgba(4,10,18,.38);
}
.exercise-table{
  width:100%;
  min-width:760px;
  border-collapse:collapse;
  font-size:.88rem;
}
.exercise-table th,.exercise-table td{
  padding:10px 12px;
  border-bottom:1px solid rgba(255,255,255,.08);
  text-align:left;
  vertical-align:top;
}
.exercise-table th{
  background:rgba(25,183,124,.14);
  color:#d9ffed;
  font-weight:850;
}
.exercise-table td{color:#e7eef9}
.exercise-table tbody tr:last-child td{border-bottom:0}
.answer-box{
  display:inline-flex;
  margin-top:12px;
  border:1px solid rgba(25,183,124,.38);
  border-radius:8px;
  background:rgba(25,183,124,.12);
  color:#d9ffed;
  padding:8px 10px;
  font-weight:800;
}
.solution-toggle{margin-top:14px}
.solution{border-top:1px solid rgba(255,255,255,.08);padding:16px;background:rgba(255,255,255,.025)}
.solution[hidden]{display:none}
.practice-grid{display:grid;gap:16px}
.step-list{display:grid;gap:10px;margin-top:14px}
.step-row{
  display:grid;
  grid-template-columns:32px minmax(0,1fr);
  gap:10px;
  align-items:start;
}
.step-number{
  display:grid;
  place-items:center;
  width:28px;
  height:28px;
  border-radius:50%;
  background:var(--blue);
  color:#fff;
  font-weight:850;
}
.tool-form{
  display:grid;
  grid-template-columns:repeat(3,minmax(0,1fr));
  gap:10px;
  margin-top:12px;
}
.tool-form label{display:grid;gap:6px;color:#d9e5f5;font-size:.9rem;font-weight:750}
.tool-form input{
  width:100%;
  border:1px solid rgba(255,255,255,.12);
  background:#0b1220;
  color:#fff;
  border-radius:8px;
  padding:9px 10px;
  font:700 .92rem/1 ui-monospace,SFMono-Regular,Menlo,Consolas,monospace;
}
.tool-result{margin-top:12px}
.result-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(170px,1fr));gap:10px}
.result-item{border:1px solid rgba(255,255,255,.08);background:#101927;border-radius:8px;padding:10px}
.result-item span{display:block;color:var(--muted);font-size:.8rem}
.result-item strong{display:block;margin-top:2px;color:#fff;font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace}
.footer{width:min(1180px,calc(100% - 36px));margin:0 auto;padding:28px 0 42px;color:var(--muted)}
@media (max-width:920px){
  .hero,.app-layout{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,.material-grid,.mini-stats,.tool-form{grid-template-columns:1fr}
  .section-heading{display:block}
  .topbar{position:relative;align-items:flex-start}
}
@media (prefers-reduced-motion:no-preference){
  .topic-card,.material-card,.content-card,.exercise-card,.tool-card{transition:transform .18s ease,border-color .18s ease}
  .topic-card:hover,.material-card:hover,.exercise-card:hover{transform:translateY(-2px);border-color:rgba(255,255,255,.18)}
}