:root{
  --accent:#1677ff;
  --accent-soft:#eaf3ff;
  --ink:#14213d;
  --muted:#66758c;
  --line:#dbe5f1;
  --paper:#fff;
  --bg:#f5f8fc;
  --good:#14805e;
  --bad:#c44444;
  font-family:"PingFang SC","Microsoft YaHei",system-ui,sans-serif;
}
*{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;color:var(--ink);background:linear-gradient(180deg,#f7faff,#fff 60%);min-height:100vh}
button,input,select{font:inherit}
button{cursor:pointer}
.topbar{position:sticky;top:0;z-index:10;display:flex;align-items:center;justify-content:space-between;gap:18px;padding:14px clamp(18px,4vw,56px);border-bottom:1px solid var(--line);background:rgba(255,255,255,.92);backdrop-filter:blur(16px)}
.brand{display:flex;align-items:center;gap:10px;font-weight:900;letter-spacing:.02em}
.brand::before{content:"";width:38px;height:38px;flex:0 0 38px;border-radius:50%;background:#fff url("chem-logo.png") center/contain no-repeat}
.back{display:inline-flex;align-items:center;gap:7px;padding:9px 14px;border:1px solid color-mix(in srgb,var(--accent) 35%,white);border-radius:12px;color:var(--accent);text-decoration:none;font-weight:800;background:#fff}
.shell{width:min(1180px,calc(100% - 32px));margin:0 auto;padding:clamp(26px,5vw,58px) 0 54px}
.hero{display:grid;grid-template-columns:minmax(0,1fr) auto;gap:24px;align-items:end;margin-bottom:24px}
.eyebrow{margin:0 0 8px;color:var(--accent);font-weight:900;letter-spacing:.08em}
h1{margin:0;font-size:clamp(32px,5vw,60px);letter-spacing:-.04em}
.lead{max-width:760px;margin:13px 0 0;color:var(--muted);font-size:clamp(15px,2vw,19px);line-height:1.75}
.badge{padding:10px 14px;border-radius:999px;color:var(--accent);background:var(--accent-soft);font-weight:800;white-space:nowrap}
.workspace{display:grid;grid-template-columns:minmax(0,1.4fr) minmax(280px,.6fr);gap:18px}
.panel{padding:clamp(18px,3vw,30px);border:1px solid var(--line);border-radius:24px;background:rgba(255,255,255,.94);box-shadow:0 18px 48px rgba(50,75,110,.08)}
.panel h2{margin:0 0 16px;font-size:21px}
.panel h3{margin:20px 0 10px;font-size:16px}
.note{padding:14px 16px;border-left:4px solid var(--accent);border-radius:10px;background:var(--accent-soft);color:#40516a;line-height:1.7}
.controls{display:grid;gap:14px}
.control{display:grid;gap:7px}
.control-row{display:flex;align-items:center;justify-content:space-between;gap:12px}
.control label{font-weight:800}
.value{color:var(--accent);font-weight:900}
input[type="range"]{width:100%;accent-color:var(--accent)}
input[type="number"],select{width:100%;padding:12px 14px;border:1px solid #cfd9e6;border-radius:12px;background:#fff;color:var(--ink);outline:none}
input:focus,select:focus{border-color:var(--accent);box-shadow:0 0 0 3px color-mix(in srgb,var(--accent) 14%,transparent)}
.primary,.secondary{border:0;border-radius:12px;padding:12px 16px;font-weight:900}
.primary{color:#fff;background:var(--accent)}
.secondary{color:var(--accent);background:var(--accent-soft)}
.button-row{display:flex;flex-wrap:wrap;gap:10px;margin-top:14px}
.result{margin-top:18px;padding:18px;border:1px dashed color-mix(in srgb,var(--accent) 40%,white);border-radius:16px;background:#fbfdff;line-height:1.7}
.result strong{color:var(--accent)}
.metric-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:10px;margin-top:16px}
.metric{padding:14px;border-radius:14px;background:var(--accent-soft)}
.metric small{display:block;color:var(--muted);margin-bottom:6px}
.metric b{font-size:20px;color:var(--accent)}
.question{font-size:20px;font-weight:900;line-height:1.55;margin:2px 0 17px}
.choices{display:grid;gap:10px}
.choice{width:100%;padding:13px 15px;border:1px solid var(--line);border-radius:13px;text-align:left;color:var(--ink);background:#fff}
.choice:hover{border-color:var(--accent);background:var(--accent-soft)}
.choice.correct{border-color:var(--good);color:var(--good);background:#ecf8f3}
.choice.wrong{border-color:var(--bad);color:var(--bad);background:#fff1f1}
.progress{height:8px;border-radius:99px;background:#e8edf4;overflow:hidden;margin-bottom:20px}
.progress i{display:block;height:100%;background:var(--accent);transition:width .25s}
.feedback{min-height:62px;margin-top:14px;padding:12px 14px;border-radius:12px;background:#f6f8fb;color:var(--muted);line-height:1.6}
.stage{position:relative;min-height:290px;border:1px solid var(--line);border-radius:20px;overflow:hidden;background:linear-gradient(#f9fcff,#eef5ff)}
.particles{position:absolute;inset:0}
.particle{position:absolute;width:10px;height:10px;border-radius:50%;background:var(--accent);opacity:.75;animation:drift var(--speed,3s) infinite alternate ease-in-out}
@keyframes drift{to{transform:translate(var(--dx,40px),var(--dy,-35px))}}
.energy-diagram{position:relative;height:250px;padding:22px}
.axis-y,.axis-x{position:absolute;background:#93a3b7}
.axis-y{left:36px;top:18px;bottom:35px;width:2px}.axis-x{left:36px;right:20px;bottom:35px;height:2px}
.energy-path{position:absolute;left:65px;right:40px;top:55px;height:130px}
.energy-path svg{width:100%;height:100%;overflow:visible}
.energy-label{position:absolute;font-weight:900;color:var(--accent)}
.scale{display:grid;grid-template-columns:repeat(15,1fr);gap:2px;margin:20px 0 8px}
.ph-cell{height:34px;display:grid;place-items:center;font-size:11px;font-weight:900;color:#fff}
.ph-cell:nth-child(-n+7){background:#d64a4a}.ph-cell:nth-child(n+8):nth-child(-n+9){background:#6a9c56}.ph-cell:nth-child(n+10){background:#3f6eb8}
.ph-cell.active{outline:4px solid #14213d;outline-offset:2px;z-index:2}
.cell-lab{position:relative;display:grid;grid-template-columns:1fr 90px 1fr;align-items:end;gap:12px;min-height:270px}
.beaker{position:relative;height:170px;border:5px solid #b9c7d8;border-top:0;border-radius:0 0 22px 22px;background:linear-gradient(transparent 22%,rgba(67,151,240,.22) 22%)}
.electrode{position:absolute;left:50%;top:-40px;width:24px;height:145px;transform:translateX(-50%);border-radius:5px;background:#8b5a2b}
.wire{position:absolute;left:50%;top:-58px;width:210px;height:80px;border:5px solid #e35b5b;border-bottom:0;border-radius:50% 50% 0 0;transform:translateX(-50%)}
.bridge{height:105px;border:14px solid #d7c9a5;border-bottom:0;border-radius:55px 55px 0 0;margin-bottom:82px}
.electron{position:absolute;top:-64px;left:16%;width:13px;height:13px;border-radius:50%;background:#ffd43b;animation:electronMove 2s linear infinite}
@keyframes electronMove{to{left:82%}}
.shells{display:grid;place-items:center;min-height:310px}
.atom{position:relative;width:260px;height:260px}
.nucleus{position:absolute;left:50%;top:50%;z-index:3;width:64px;height:64px;display:grid;place-items:center;transform:translate(-50%,-50%);border-radius:50%;color:#fff;background:var(--accent);font-weight:900}
.orbit{position:absolute;left:50%;top:50%;border:2px solid #9fb1c8;border-radius:50%;transform:translate(-50%,-50%)}
.electron-dot{position:absolute;width:12px;height:12px;border:2px solid #fff;border-radius:50%;background:#ff9f1c;box-shadow:0 0 0 1px #ff9f1c}
.periodic-grid{display:grid;grid-template-columns:repeat(18,minmax(34px,1fr));gap:4px;overflow:auto}
.element{min-width:34px;aspect-ratio:1;padding:3px;border:1px solid var(--line);border-radius:7px;background:#fff;text-align:center;font-size:10px}
.element b{display:block;color:var(--accent);font-size:14px}
.element.empty{visibility:hidden}
.element:hover,.element.active{color:#fff;background:var(--accent);border-color:var(--accent)}
.element:hover b,.element.active b{color:#fff}
.molecule{position:relative;width:300px;height:270px;margin:auto;perspective:600px}
.atom-ball{position:absolute;z-index:2;width:56px;height:56px;display:grid;place-items:center;border-radius:50%;color:#fff;background:radial-gradient(circle at 35% 30%,#7ea7d9,#183d6d 65%);box-shadow:0 12px 20px rgba(20,33,61,.25);font-weight:900}
.atom-ball.center{left:122px;top:105px;width:62px;height:62px;background:radial-gradient(circle at 35% 30%,#626b78,#151a22 68%)}
.bond{position:absolute;z-index:1;height:10px;border-radius:99px;background:linear-gradient(#eef3f8,#9daec2);transform-origin:left center}
.info-list{display:grid;gap:10px;margin:0;padding:0;list-style:none}
.info-list li{padding:11px 13px;border-radius:11px;background:#f6f8fb;line-height:1.55}
.equation-builder{display:flex;align-items:center;justify-content:center;flex-wrap:wrap;gap:10px;min-height:150px;padding:22px;border:1px solid var(--line);border-radius:18px;background:#f8fbff}
.formula-unit{display:flex;align-items:center;gap:6px;font-size:25px;font-weight:900}
.formula-unit input{width:62px;padding:10px 6px;text-align:center}
.operator{color:var(--muted);font-size:24px;font-weight:900}
.atom-check{display:grid;grid-template-columns:repeat(auto-fit,minmax(100px,1fr));gap:9px;margin-top:14px}
.atom-count{padding:10px;border-radius:10px;background:#f6f8fb;text-align:center}
.atom-count.ok{color:var(--good);background:#ecf8f3}
.titration-chart{position:relative;height:330px;margin-top:14px;padding:14px;border:1px solid var(--line);border-radius:18px;background:#fbfdff}
.titration-chart svg{width:100%;height:100%}
.chart-label{fill:#68788d;font-size:12px}
.chart-guide{stroke:#d6e0ec;stroke-width:1;stroke-dasharray:5 5}
.chart-curve{fill:none;stroke:var(--accent);stroke-width:5;stroke-linecap:round;stroke-linejoin:round}
.chart-point{fill:#fff;stroke:var(--accent);stroke-width:4}
.footer-note{margin-top:26px;text-align:center;color:#8190a4;font-size:13px}
@media(max-width:820px){
  .hero,.workspace{grid-template-columns:1fr}
  .badge{justify-self:start}
  .workspace{gap:14px}
  .metric-grid{grid-template-columns:1fr}
  .periodic-grid{grid-template-columns:repeat(18,42px)}
}