:root{
  --paper:#FBFCFA;
  --panel:#F3F6F3;
  --ink:#16201C;
  --ink-soft:#4A5751;
  --teal:#0E7C6B;
  --teal-deep:#0A5F52;
  --amber:#C77A28;
  --amber-wash:rgba(199,122,40,.12);
  --line:#DCE3DE;
  --atp:#C0392B;
  --fbp:#2C6E8F;
  --pep:#2A2F2C;
  --maxw:74ch;
}

*{box-sizing:border-box}
html,body{margin:0}
body{
  background:var(--paper);
  color:var(--ink);
  font-family:"Inter",system-ui,sans-serif;
  font-size:16px;
  line-height:1.5;
  -webkit-font-smoothing:antialiased;
}

/* ---------- Top bar ---------- */
.topbar{
  display:flex;align-items:center;justify-content:space-between;gap:1.5rem;
  padding:.85rem 1.5rem;
  border-bottom:1px solid var(--line);
  background:var(--paper);
  position:sticky;top:0;z-index:10;
  flex-wrap:wrap;
}
.brand{display:flex;align-items:center;gap:.9rem}
.pathway{width:150px;height:22px}
.pathway line{stroke:var(--line);stroke-width:2}
.pathway circle{fill:var(--teal)}
.pathway circle.glu{fill:var(--amber)}
.pathway circle.out{fill:var(--teal-deep)}
.titles h1{
  font-family:"Spectral",Georgia,serif;
  font-weight:600;font-size:1.15rem;margin:0;font-style:italic;
  letter-spacing:.1px;
}
.titles p{margin:.1rem 0 0;font-size:.78rem;color:var(--ink-soft)}

.tabs{display:flex;gap:.35rem}
.tabs button{
  font:inherit;font-size:.9rem;
  border:1px solid transparent;border-radius:7px;
  padding:.4rem .85rem;background:none;color:var(--ink-soft);cursor:pointer;
}
.tabs button:hover{background:var(--panel);color:var(--ink)}
.tabs button.active{background:var(--teal);color:#fff}

/* ---------- Views ---------- */
main{max-width:1180px;margin:0 auto;padding:1.5rem}
.view{display:none}
.view.active{display:grid}

#view-lessons{grid-template-columns:230px 1fr;gap:2rem;align-items:start}
#view-sim{grid-template-columns:320px 1fr;gap:1.75rem;align-items:start}
#view-model{grid-template-columns:1fr}

/* ---------- Lesson nav ---------- */
.lesson-nav h2,.controls h2{
  font-family:"Spectral",serif;font-size:1rem;font-weight:600;
  margin:.2rem 0 .8rem;color:var(--teal-deep);
}
#lesson-list{list-style:none;margin:0;padding:0;counter-reset:l}
#lesson-list li{margin:0 0 .3rem}
#lesson-list button{
  counter-increment:l;
  display:flex;gap:.6rem;align-items:baseline;width:100%;text-align:left;
  font:inherit;font-size:.92rem;cursor:pointer;
  border:1px solid var(--line);border-radius:8px;background:#fff;
  padding:.55rem .7rem;color:var(--ink);
}
#lesson-list button::before{
  content:counter(l);
  font-family:"Spectral",serif;font-weight:600;color:var(--amber);
  min-width:1ch;
}
#lesson-list button:hover{border-color:var(--teal)}
#lesson-list button.active{border-color:var(--teal);background:var(--panel)}

/* ---------- Prose (lesson) ---------- */
.prose{
  max-width:var(--maxw);
  font-family:"Spectral",Georgia,serif;
  font-size:1.06rem;line-height:1.68;
}
.prose h1{font-size:1.7rem;font-weight:600;line-height:1.2;margin:.2rem 0 1rem}
.prose h2{font-size:1.3rem;font-weight:600;margin:2rem 0 .6rem;color:var(--teal-deep)}
.prose h3{font-size:1.08rem;font-weight:600;margin:1.4rem 0 .4rem}
.prose p{margin:.7rem 0}
.prose blockquote{
  margin:1rem 0;padding:.6rem 1rem;
  border-left:3px solid var(--teal);
  background:var(--panel);border-radius:0 8px 8px 0;
  font-size:.98rem;
}
.prose code{
  font-family:"SFMono-Regular",Menlo,Consolas,monospace;
  font-size:.86em;background:var(--panel);padding:.1em .35em;border-radius:4px;
}
.prose table{border-collapse:collapse;margin:1rem 0;font-size:.95rem;width:100%}
.prose th,.prose td{border:1px solid var(--line);padding:.4rem .6rem;text-align:left}
.prose th{background:var(--panel);font-family:"Inter",sans-serif}
.prose hr{border:none;border-top:1px solid var(--line);margin:1.6rem 0}
.prose a{color:var(--teal-deep)}

/* ---------- Sim controls ---------- */
.controls{
  background:var(--panel);border:1px solid var(--line);border-radius:12px;
  padding:1.1rem;position:sticky;top:5rem;
}
.controls fieldset{
  border:1px solid var(--line);border-radius:9px;margin:.9rem 0;padding:.6rem .8rem;
}
.controls legend{font-size:.8rem;color:var(--ink-soft);padding:0 .3rem}
.controls label{display:flex;justify-content:space-between;align-items:center;
  gap:.6rem;font-size:.9rem;margin:.35rem 0}
.controls input[type=number]{
  width:5.5rem;font:inherit;padding:.28rem .4rem;
  border:1px solid var(--line);border-radius:6px;background:#fff;text-align:right;
}
.controls label.switch{cursor:pointer;justify-content:flex-start;gap:.5rem}
.switch input{accent-color:var(--teal);width:1rem;height:1rem}
.chips{display:flex;flex-wrap:wrap;gap:.35rem}
.chips label{
  display:inline-flex;gap:.3rem;align-items:center;justify-content:flex-start;
  font-size:.82rem;border:1px solid var(--line);border-radius:20px;
  padding:.2rem .55rem;background:#fff;margin:0;
}
.chips input{accent-color:var(--teal)}

button.primary{
  width:100%;margin-top:.4rem;font:inherit;font-weight:500;
  background:var(--teal);color:#fff;border:none;border-radius:9px;
  padding:.6rem;cursor:pointer;
}
button.primary:hover{background:var(--teal-deep)}
button.primary:disabled{opacity:.55;cursor:progress}

button.secondary{
  width:100%;margin-top:.5rem;font:inherit;font-weight:500;
  background:#fff;color:var(--teal-deep);border:1px solid var(--teal);
  border-radius:9px;padding:.6rem;cursor:pointer;
}
button.secondary:hover{background:var(--panel)}
button.secondary:disabled{opacity:.55;cursor:progress}
.muted.small{font-size:.78rem;margin-top:.85rem;line-height:1.45}

/* ---------- Monte-Carlo ---------- */
#view-mc{grid-template-columns:320px 1fr;gap:1.75rem;align-items:start}
.mc-results{min-width:0}
#mc-table{border-collapse:collapse;width:100%;font-size:.92rem;margin-bottom:1.4rem}
#mc-table th,#mc-table td{border:1px solid var(--line);padding:.5rem .7rem;text-align:left}
#mc-table th{background:var(--panel);font-family:"Inter",sans-serif}
#mc-table td.bm{color:var(--ink-soft);font-size:.85em;white-space:nowrap}
#mc-table .sub{color:var(--ink-soft);font-size:.82em}
.mc-figs{display:grid;grid-template-columns:1fr 1fr;gap:1.1rem}
.mc-figs figure{margin:0;min-width:0}
.mc-figs figcaption{
  font-family:"Spectral",serif;font-weight:600;color:var(--teal-deep);
  font-size:.98rem;margin-bottom:.35rem;
}
.mc-figs figcaption span{
  font-family:"Inter",sans-serif;font-weight:400;color:var(--ink-soft);font-size:.78rem;
}
.mc-figs > figure > div{width:100%;height:300px}
.fignote{
  font-size:.8rem;line-height:1.5;color:var(--ink-soft);
  margin:.5rem 0 0;padding:.5rem .7rem;
  background:var(--panel);border-left:3px solid var(--amber);border-radius:0 6px 6px 0;
}
.fignote b{color:var(--ink)}

.plot-wrap{min-height:460px}
#plot{width:100%;height:460px}
.caption{font-size:.85rem;color:var(--ink-soft);margin-top:.6rem;max-width:70ch}
.muted{color:var(--ink-soft);font-size:.88rem}

/* ---------- Model panel ---------- */
.stats{display:flex;gap:1.5rem;flex-wrap:wrap;margin-bottom:1.2rem}
.stat{background:var(--panel);border:1px solid var(--line);border-radius:10px;
  padding:.7rem 1rem;min-width:7rem}
.stat b{display:block;font-family:"Spectral",serif;font-size:1.5rem;color:var(--teal-deep)}
.stat span{font-size:.8rem;color:var(--ink-soft)}
#reaction-table{border-collapse:collapse;width:100%;font-size:.9rem}
#reaction-table th,#reaction-table td{border:1px solid var(--line);padding:.4rem .6rem;text-align:left}
#reaction-table th{background:var(--panel)}
#reaction-table td.flux{text-align:right;font-variant-numeric:tabular-nums}
#reaction-table code{font-size:.85em}

/* ---------- Responsive ---------- */
@media (max-width:820px){
  #view-lessons,#view-sim,#view-mc{grid-template-columns:1fr}
  .controls{position:static}
  .mc-figs{grid-template-columns:1fr}
}
@media (prefers-reduced-motion:reduce){*{transition:none!important}}