:root{--navy:#0d2b45;--blue:#2c6f9f;--brick:#bf512e;--bg:#f3f7f9;--paper:#fff;--ink:#173047;--muted:#728591;--line:#d7e2e8;--good:#e4f4e8;--bad:#fde9e5;--hint:#fff7dd}
*{box-sizing:border-box}body{margin:0;background:var(--bg);font-family:Inter,system-ui,-apple-system,"Segoe UI",Arial,sans-serif;color:var(--ink)}button,input{font:inherit}
.top{background:var(--navy);color:#fff}.top>div{max-width:1180px;margin:auto;height:48px;padding:0 17px;display:flex;align-items:center;gap:9px}.top a{color:#fff;text-decoration:none;font-size:12px;font-weight:850}.top span{opacity:.55}.top .copy{margin-left:auto;border:1px solid rgba(255,255,255,.28);background:none;color:#fff;border-radius:8px;padding:6px 9px;font-weight:850;cursor:pointer}
.wrap{max-width:1180px;margin:auto;padding:19px 17px 52px}.hero{background:#fff;border:1px solid var(--line);border-radius:18px;padding:23px 25px;box-shadow:0 9px 24px rgba(13,43,69,.055)}
.course{display:inline-flex;align-items:center;gap:7px;background:#f2e9e5;color:#a64629;border-radius:999px;padding:5px 8px;font-size:10px;font-weight:950;text-transform:uppercase;letter-spacing:.06em}.hero h1{margin:8px 0 5px;color:var(--navy);font-size:clamp(28px,4.8vw,46px);line-height:1.05}.hero>p{margin:0;color:var(--muted)}
.meta{display:grid;grid-template-columns:1.2fr .8fr;gap:10px;margin-top:14px}.box{background:#f8fafb;border:1px solid #e4ebef;border-radius:11px;padding:11px}.box b{display:block;color:var(--navy);font-size:11px;margin-bottom:5px}.box ul{margin:0;padding-left:18px;color:#5e7280;font-size:11px;line-height:1.5}.box span{color:#5e7280;font-size:11px;line-height:1.5}
.levels{display:flex;gap:6px;flex-wrap:wrap;margin-top:13px;align-items:center}.lvl{border:1px solid var(--line);background:#fff;color:#4d6778;border-radius:8px;padding:7px 9px;font-weight:900;cursor:pointer}.lvl.active{background:var(--blue);color:#fff;border-color:var(--blue)}.help{margin-left:auto;font-size:11px;font-weight:800;color:#5c7281}
.layout{display:grid;grid-template-columns:255px minmax(0,1fr);gap:13px;margin-top:13px}.side,.task{background:#fff;border:1px solid var(--line);border-radius:15px;box-shadow:0 7px 18px rgba(13,43,69,.045)}.side{padding:11px;height:fit-content;position:sticky;top:12px}.side h2{font-size:9px;letter-spacing:.09em;text-transform:uppercase;color:#8a99a3;margin:3px 6px 7px}.mode{width:100%;display:block;border:0;background:transparent;text-align:left;padding:8px 9px;border-radius:8px;color:#39596e;font-weight:850;cursor:pointer}.mode:hover{background:#f4f8fa}.mode.active{background:#e8f2f7;color:#195a87}.mode small{display:block;font-size:9px;color:#8b99a3;font-weight:650;margin-top:2px}.statbar{display:flex;gap:5px;flex-wrap:wrap;margin-top:9px}.stat{font-size:9px;background:#f3f6f8;color:#71828d;border-radius:999px;padding:4px 6px}
.task{padding:20px;min-height:540px}.taskhead{display:flex;align-items:center;justify-content:space-between}.pill{background:#edf4f7;color:#265e85;border-radius:999px;padding:5px 8px;font-size:10px;font-weight:900}.counter{font-size:10px;color:#8b99a3}.question{text-align:center;color:var(--navy);font-size:clamp(21px,3.6vw,31px);font-weight:950;margin:28px 0 15px;line-height:1.2}.sub{text-align:center;color:var(--muted);font-size:12px;line-height:1.5;margin:-6px auto 15px;max-width:760px}.expr{text-align:center;color:var(--navy);font-size:clamp(31px,6vw,52px);font-weight:950;margin:16px 0}
.answerrow{display:flex;gap:7px;justify-content:center;align-items:center;flex-wrap:wrap}.answer{width:190px;border:2px solid #b9cad5;border-radius:9px;padding:8px;text-align:center;font-size:19px;font-weight:900}.btn{border:0;border-radius:8px;padding:8px 11px;font-weight:900;cursor:pointer}.primary{background:var(--blue);color:#fff}.secondary{background:#fff;border:1px solid var(--line);color:var(--navy)}
.choices{display:grid;gap:7px;max-width:720px;margin:auto}.choice{border:1px solid #c6d3dc;background:#fff;border-radius:9px;padding:9px 11px;color:#36576c;font-weight:850;cursor:pointer;text-align:center}.choice:hover{background:#f5f8fa}.correct{background:var(--good)!important;border-color:#78a685!important}.wrong{background:var(--bad)!important;border-color:#c97066!important}
.feedback{display:none;max-width:760px;margin:13px auto 0;padding:9px 11px;border-radius:9px;text-align:center;font-size:12px;font-weight:850}.feedback.show{display:block}.feedback.good{background:var(--good);color:#2d6740}.feedback.bad{background:var(--bad);color:#963c33}.hintbox{max-width:780px;margin:10px auto;background:var(--hint);border:1px solid #ead282;border-radius:9px;padding:9px 10px;color:#705b16;font-size:11px;line-height:1.45}
.grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:7px;max-width:720px;margin:auto}.cell{background:#f8fafb;border:1px solid var(--line);border-radius:9px;padding:9px;display:grid;grid-template-columns:1fr 100px;gap:7px;align-items:center;font-size:11px;font-weight:800}.cell input{width:100%;border:2px solid #bdcbd4;border-radius:7px;padding:6px;text-align:center;font-weight:850}
.visual{max-width:720px;margin:11px auto;background:#fafcfd;border:1px solid var(--line);border-radius:11px;padding:10px;text-align:center}.actions{display:flex;justify-content:space-between;gap:8px;flex-wrap:wrap;margin-top:17px}.summary{text-align:center;max-width:700px;margin:34px auto}.summary h2{color:var(--navy);font-size:28px}.summary p{color:var(--muted)}
.frac{display:inline-grid;vertical-align:-.35em;grid-template-rows:auto auto;line-height:1;text-align:center;margin:0 .08em}.frac .n{border-bottom:.075em solid currentColor;padding:0 .12em .07em}.frac .d{padding:.07em .12em 0}
@media(max-width:820px){.layout{grid-template-columns:1fr}.side{position:static}.meta{grid-template-columns:1fr}.grid{grid-template-columns:1fr}.help{margin-left:0}.task{min-height:auto}}