:root{--ink:#18212f;--muted:#697386;--line:#dfe4ea;--soft:#f5f7fa;--blue:#2563eb;--blue-dark:#1849b9;--blue-soft:#eaf1ff;--green:#16865c;--green-soft:#e7f6ef;--amber:#c86f17;--amber-soft:#fff3df;--red:#c53d51;--red-soft:#ffebee;--navy:#15253f;--white:#fff;font-family:Inter,"PingFang SC","Microsoft YaHei",Arial,sans-serif;color:var(--ink);background:#edf1f6;font-synthesis:none}*{box-sizing:border-box}body{margin:0;min-width:320px}button,select,input{font:inherit}button{cursor:pointer}.app{min-height:100vh;display:grid;grid-template-columns:264px minmax(0,1fr);background:white}.sidebar{min-height:100vh;padding:30px 22px;background:var(--navy);color:white;display:flex;flex-direction:column}.brand{border:0;background:transparent;color:white;display:flex;align-items:center;gap:12px;text-align:left;font-size:19px;font-weight:800}.brand-mark{width:38px;height:38px;border-radius:8px;background:#f4c95d;color:var(--navy);display:grid;place-items:center;font-size:21px}.brand-name small{display:block;margin-top:2px;color:#aebbd0;font-size:11px}.nav-label{margin:44px 10px 12px;color:#8fa0b9;font-size:11px;font-weight:800}.nav-item{width:100%;border:0;border-radius:7px;padding:12px 14px;display:flex;gap:11px;align-items:center;color:#c8d2e2;background:transparent;text-align:left}.nav-item.active{background:#263957;color:white}.nav-icon{width:22px;font-size:17px;text-align:center}.student{margin-top:auto;padding:15px;border:1px solid #344966;border-radius:8px;display:flex;align-items:center;gap:10px}.avatar{width:34px;height:34px;border-radius:50%;background:#f4c95d;color:var(--navy);display:grid;place-items:center;font-weight:800}.student-copy b,.student-copy small{display:block}.student-copy b{font-size:13px}.student-copy small{color:#9dabc0;font-size:11px;margin-top:3px}.main{min-width:0;background:#f8fafc}.topbar{height:72px;padding:0 42px;border-bottom:1px solid var(--line);background:rgba(255,255,255,.96);display:flex;align-items:center;justify-content:space-between}.crumb{color:var(--muted);font-size:13px}.crumb strong{color:var(--ink)}.top-actions{display:flex;align-items:center;gap:10px}.status-pill{padding:6px 9px;background:var(--green-soft);color:var(--green);border-radius:6px;font-size:11px;font-weight:800}.icon-button{width:38px;height:38px;border:1px solid var(--line);border-radius:7px;background:white;color:var(--ink)}.screen{padding:42px;max-width:1280px;margin:0 auto}.eyebrow{color:var(--blue);font-size:12px;font-weight:800}h1{font-size:32px;line-height:1.25;letter-spacing:0;margin:8px 0 10px}h2{font-size:21px;letter-spacing:0;margin:0}p{color:var(--muted);line-height:1.65}.intro{max-width:680px;margin:0 0 30px}.panel{background:white;border:1px solid var(--line);border-radius:8px}.setup-grid{display:grid;grid-template-columns:minmax(0,1.25fr) minmax(300px,.75fr);gap:28px}.form-panel{padding:30px}.field{margin-top:24px}.field label{display:block;margin-bottom:9px;font-size:13px;font-weight:700}.field select{width:100%;height:52px;padding:0 15px;border:1px solid #cdd4de;border-radius:7px;background:white}.primary,.secondary{min-height:48px;padding:0 20px;border-radius:7px;font-weight:800}.primary{border:0;background:var(--blue);color:white}.primary:hover{background:var(--blue-dark)}.primary:disabled{background:#aab5c8;cursor:not-allowed}.secondary{border:1px solid #cbd3de;background:white;color:var(--ink)}.full{width:100%;margin-top:28px}.preview-panel{overflow:hidden}.preview-art{height:250px;padding:30px;background:#eaf1ff;display:grid;place-items:center}.formula{width:220px;height:160px;position:relative}.formula-card{position:absolute;padding:13px 17px;border:1px solid #b8c9eb;border-radius:7px;background:white;box-shadow:0 10px 25px rgba(29,62,119,.12);font-weight:800}.formula-card.one{top:8px;left:0;transform:rotate(-5deg)}.formula-card.two{right:0;top:55px;transform:rotate(6deg)}.formula-card.three{left:42px;bottom:0;color:var(--blue)}.preview-copy{padding:24px 26px}.preview-copy p{font-size:13px;margin-bottom:0}.path-header{display:flex;align-items:end;justify-content:space-between;gap:24px;margin-bottom:26px}.progress-copy{min-width:210px}.progress-row{display:flex;justify-content:space-between;margin-bottom:9px;font-size:12px;font-weight:700}.progress-track{height:8px;border-radius:8px;background:#e5e9ef;overflow:hidden}.progress-track span{display:block;height:100%;background:var(--green)}.level-list{display:grid;gap:12px}.level{min-height:94px;padding:18px 20px;display:grid;grid-template-columns:52px minmax(0,1fr) auto;gap:16px;align-items:center;background:white;border:1px solid var(--line);border-radius:8px}.level.current{border:2px solid var(--blue);background:#fbfdff}.level.locked{color:#8b95a5;background:#f3f5f7}.level-number{width:45px;height:45px;border-radius:50%;background:var(--blue-soft);color:var(--blue);display:grid;place-items:center;font-weight:900}.level.completed .level-number{background:var(--green);color:white}.level.locked .level-number{background:#e4e8ed;color:#8b95a5}.level-title{font-weight:800;margin-bottom:6px}.level-meta{color:var(--muted);font-size:12px}.tag{padding:6px 10px;border-radius:6px;background:var(--blue-soft);color:var(--blue);font-size:11px;font-weight:800}.tag.done{background:var(--green-soft);color:var(--green)}.tag.lock{background:#e5e8ec;color:#747e8e}.difficulty-grid{margin-top:28px;display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:16px}.difficulty{min-height:155px;padding:24px;text-align:left;border:1px solid var(--line);border-radius:8px;background:white;position:relative;transition:.18s ease}.difficulty:hover{transform:translateY(-2px);box-shadow:0 12px 24px rgba(33,45,69,.08)}.difficulty .symbol{width:42px;height:42px;border-radius:8px;display:grid;place-items:center;font-size:20px;margin-bottom:17px}.difficulty strong{font-size:18px}.difficulty p{margin:6px 0 0;font-size:12px}.difficulty .arrow{position:absolute;right:22px;top:25px;font-size:20px}.easy .symbol{background:var(--green-soft);color:var(--green)}.medium .symbol{background:var(--blue-soft);color:var(--blue)}.hard .symbol{background:var(--amber-soft);color:var(--amber)}.hell .symbol{background:var(--red-soft);color:var(--red)}.quiz-shell{max-width:850px;margin:0 auto}.quiz-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:12px}.quiz-progress{display:grid;grid-template-columns:repeat(5,1fr);gap:7px}.quiz-progress span{height:6px;border-radius:6px;background:#dfe4ea}.quiz-progress span.done{background:var(--blue)}.question{margin-top:28px;padding:34px}.question-type{color:var(--blue);font-size:12px;font-weight:800}.stem{font-size:24px;font-weight:800;margin:13px 0 28px}.options{display:grid;gap:11px}.option{min-height:58px;padding:0 17px;border:1px solid #d7dde5;border-radius:7px;background:white;display:flex;align-items:center;gap:13px;text-align:left}.option.selected{border:2px solid var(--blue);background:var(--blue-soft)}.letter{width:30px;height:30px;border-radius:50%;border:1px solid #cbd3de;display:grid;place-items:center;font-size:12px;font-weight:800;flex:0 0 auto}.selected .letter{background:var(--blue);border-color:var(--blue);color:white}.quiz-actions{margin-top:20px;display:flex;justify-content:space-between}.score-layout{display:grid;grid-template-columns:310px minmax(0,1fr);gap:24px;align-items:start}.score-summary{padding:30px;text-align:center}.score-ring{width:150px;height:150px;margin:10px auto 20px;border-radius:50%;display:grid;place-items:center}.score-inner{width:120px;height:120px;border-radius:50%;background:white;display:grid;place-items:center}.score-inner strong{font-size:43px}.score-inner span{display:block;color:var(--muted);font-size:11px}.score-facts{display:flex;border-top:1px solid var(--line);margin-top:24px;padding-top:18px}.score-facts div{flex:1}.score-facts div+div{border-left:1px solid var(--line)}.score-facts strong,.score-facts span{display:block}.score-facts span{margin-top:4px;color:var(--muted);font-size:11px}.review{padding:26px}.review-list{display:flex;gap:9px;margin:20px 0;flex-wrap:wrap}.review-dot{width:44px;height:40px;border-radius:7px;display:grid;place-items:center;background:var(--green-soft);color:var(--green);font-weight:900}.review-dot.wrong{background:var(--red-soft);color:var(--red)}.mistake{padding:18px;border:1px solid #efcbd1;border-radius:7px;background:#fffafb;margin-top:12px}.mistake strong{display:block;margin-bottom:12px}.answer-line{display:flex;gap:28px;color:var(--muted);font-size:13px;flex-wrap:wrap}.answer-line b{color:var(--ink)}.score-actions{display:flex;gap:10px;margin-top:22px}.score-actions button{flex:1}.loading{min-height:430px;display:grid;place-items:center;text-align:center}.spinner{width:42px;height:42px;border:4px solid #dbe4f4;border-top-color:var(--blue);border-radius:50%;margin:0 auto 18px;animation:spin .8s linear infinite}@keyframes spin{to{transform:rotate(360deg)}}.empty{padding:60px;text-align:center}.toast{position:fixed;left:50%;bottom:28px;transform:translate(-50%,20px);padding:12px 16px;border-radius:7px;background:#1e293b;color:white;font-size:13px;opacity:0;pointer-events:none;transition:.2s;z-index:30}.toast.show{opacity:1;transform:translate(-50%,0)}.modal-backdrop{position:fixed;inset:0;background:rgba(13,23,40,.45);display:grid;place-items:center;padding:24px;z-index:40}.modal{width:min(440px,100%);padding:26px;background:white;border-radius:8px}.modal-actions{display:flex;justify-content:flex-end;gap:10px;margin-top:22px}.error-box{padding:20px;border:1px solid #efcbd1;background:#fffafb;border-radius:8px}.skeleton{height:94px;border-radius:8px;background:linear-gradient(90deg,#edf0f4,#f8fafc,#edf0f4);background-size:200% 100%;animation:shimmer 1.2s infinite}@keyframes shimmer{to{background-position:-200% 0}}
@media(max-width:1100px){.app{grid-template-columns:84px minmax(0,1fr)}.sidebar{padding:24px 14px;align-items:center}.brand-name,.nav-label,.nav-item span:not(.nav-icon),.student-copy{display:none}.nav-item{justify-content:center;padding:12px}.student{padding:10px}.topbar{padding:0 28px}.screen{padding:32px 28px}.setup-grid{grid-template-columns:1fr}.preview-panel{display:none}.score-layout{grid-template-columns:1fr}.score-summary{display:grid;grid-template-columns:180px 1fr;align-items:center;text-align:left}.score-facts{margin:0;border-top:0;padding-top:0}}
@media(max-width:620px){.app{display:block}.sidebar{display:none}.topbar{height:60px;padding:0 18px}.status-pill{display:none}.screen{padding:24px 18px 90px}h1{font-size:27px}.difficulty-grid{grid-template-columns:1fr}.path-header{align-items:start;flex-direction:column}.progress-copy{width:100%}.level{grid-template-columns:45px minmax(0,1fr)}.level>:last-child{grid-column:2;justify-self:start}.question{padding:24px 18px}.stem{font-size:20px}.score-summary{display:block;text-align:center}.score-facts{margin-top:20px;padding-top:18px;border-top:1px solid var(--line)}.score-actions{flex-direction:column-reverse}}