*{box-sizing:border-box}
:root{--bg:#fbfcfa;--fg:#263b33;--muted:#768178;--line:#e1e6df;--accent:#e99b3e;--accent-ink:#b8742a;--ok:#4e7148}
body{margin:0;background:var(--bg);color:var(--fg);font:15px/1.7 -apple-system,BlinkMacSystemFont,"PingFang SC","Microsoft YaHei",sans-serif;-webkit-font-smoothing:antialiased}
button,input{font:inherit}
button{cursor:pointer}
button:focus-visible,input:focus-visible{outline:2px solid var(--accent);outline-offset:3px}
.lesson{max-width:1100px;margin:0 auto;padding:24px 20px 32px}
.eyebrow,.kicker{font-size:11px;letter-spacing:1.5px;color:#7c8f7f}
h1{font-size:clamp(22px,3.4vw,29px);line-height:1.5;margin:8px 0 6px;letter-spacing:-.4px}
.heading p{margin:0 0 20px;color:var(--muted);font-size:14px}
.workbench{background:#fff;border:1px solid var(--line);border-radius:12px;overflow:hidden}
.toolbar{display:flex;justify-content:space-between;align-items:center;padding:12px 18px;border-bottom:1px solid #edf0ea;font-size:12px;color:#607457;gap:10px}
.toolbar em{font-style:normal;color:#9aa491}
.live-dot{display:inline-block;width:6px;height:6px;border-radius:50%;background:#82a775;margin-right:8px;vertical-align:middle}
.text-button{border:0;background:none;color:#778a6b;font-size:12px;padding:6px 0}
.stage{display:grid;grid-template-columns:minmax(0,1fr) 220px;align-items:center}
#scene{width:100%;height:auto;display:block;background:#fcfbf7}
.readouts{display:flex;flex-direction:column;gap:10px;padding:18px}
.readouts div{border:1px solid #efe9de;border-radius:10px;padding:10px 12px;background:#fffdf9}
.readouts span{display:block;font-size:11px;color:var(--muted)}
.readouts strong{font-size:20px;font-weight:600;font-variant-numeric:tabular-nums;color:var(--accent-ink)}
.controls{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:22px 28px;padding:20px 22px;border-top:1px solid #edf0ea}
.range span{display:flex;justify-content:space-between;font-size:12px;color:#829275;margin-bottom:6px}
.range output{font-size:15px;color:#506c45;font-variant-numeric:tabular-nums}
.range input{width:100%;accent-color:var(--accent);height:28px}
.presets{grid-column:1/-1;display:flex;gap:8px;align-items:center;font-size:12px;color:#8c9b7f}
.presets span{margin-right:6px}
.presets button{min-height:36px;padding:4px 12px;border:1px solid #e1e9d8;background:#f9fbf6;color:#6b835a;border-radius:6px;font-size:12px}
.presets button[aria-pressed=true]{background:#4e7148;border-color:#4e7148;color:#fff}
.footnote{margin:0;padding:10px 22px;border-top:1px solid #f0f2eb;font-size:11px;color:#97a08e}
.challenge{display:flex;gap:18px;align-items:center;margin-top:20px;padding:20px;border:1px solid #e0e7d7;background:#f6f8f0;border-radius:10px}
.challenge.done{background:#f0f7ed;border-color:#cfdfc7}
.challenge-icon{width:42px;height:42px;flex-shrink:0;display:grid;place-items:center;background:#e9efdf;color:#80945f;border-radius:10px;font-size:18px}
.challenge-body{flex:1;min-width:0}
.challenge h2{font-size:15px;font-weight:500;margin:6px 0 4px}
.challenge p{font-size:13px;color:#7d8c6c;margin:0}
.options{display:flex;flex-wrap:wrap;gap:8px;margin-top:10px}
.options button,.secondary-button{min-height:40px;border:1px solid #d5dfca;background:#fff;padding:8px 14px;font-size:13px;border-radius:6px;color:#60794f}
.options button.picked{background:#4e7148;border-color:#4e7148;color:#fff}
.secondary-button[hidden]{display:none}
@media (max-width:720px){
  .stage{grid-template-columns:1fr}
  .readouts{flex-direction:row;padding:12px}
  .readouts div{flex:1;padding:8px}
  .readouts strong{font-size:16px}
  .controls{grid-template-columns:1fr}
  .challenge{flex-direction:column;align-items:flex-start}
}
@media (prefers-reduced-motion:reduce){*{transition:none!important}}

/* ---- photosynthesis additions ---- */
:root{--accent:#4f9a5a;--accent-ink:#3a7a45}
.range input{accent-color:#4f9a5a}
.side{display:flex;flex-direction:column;gap:12px;padding:16px}
.side .readouts{padding:0}
.readouts .big strong{font-size:30px}
.readouts small{font-size:11px;color:var(--muted)}
.equation{border:1px dashed #cfe0cc;border-radius:10px;padding:10px 12px;font-family:Georgia,"Times New Roman",serif;font-size:14px;color:#3f6f49;display:flex;flex-wrap:wrap;align-items:center;gap:4px;line-height:1.4}
.equation .arrow{font-size:10px;text-align:center;line-height:1.15;color:#8aa58a;padding:0 2px;font-family:inherit}
.equation span{transition:color .3s,background .3s;border-radius:4px;padding:0 2px}
.equation .hot{background:#fff3c4;color:#8a6a10}
.equation .dim{color:#c2cfc2}
.chart-wrap{border-top:1px solid #edf0ea;padding:8px 14px 0;background:#fcfdfb}
#chart{width:100%;height:auto;display:block}
.stage{grid-template-columns:minmax(0,1fr) 250px}
.presets{flex-wrap:wrap}
@media (max-width:720px){.stage{grid-template-columns:1fr}.side{padding:12px}}
/* SVG text scales with the viewBox; keep labels legible on phones. */
@media (max-width:720px){
  #scene text{font-size:22px}
  #chart text{font-size:19px}
}