*,:after,:before{box-sizing:border-box;margin:0;padding:0}:root{--bg:#0f1117;--surface:#1a1d27;--surface2:#22263a;--border:#2e3348;--text:#e8eaf0;--muted:#8b93b0;--blue:#4f8ef7;--blue-dim:#1e3a6e;--green:#3ecf8e;--green-dim:#0d3d2a;--red:#f26b6b;--red-dim:#3d1515;--amber:#f5a623;--amber-dim:#3d2800;--radius:10px;--radius-sm:6px}body{background:var(--bg);color:var(--text);font-family:-apple-system,BlinkMacSystemFont,Segoe UI,sans-serif;font-size:15px;line-height:1.6;min-height:100vh}a{color:var(--blue);text-decoration:none}a:hover{text-decoration:underline}.container{max-width:900px;margin:0 auto;padding:0 20px}.nav{background:var(--surface);border-bottom:1px solid var(--border);padding:0 20px;height:56px;display:flex;align-items:center;justify-content:space-between;position:-webkit-sticky;position:sticky;top:0;z-index:100}.nav-brand{font-size:17px;font-weight:600;color:var(--text)}.nav-brand span{color:var(--blue)}.nav-links{display:flex;align-items:center;gap:16px}.btn-nav,.nav-user{font-size:13px;color:var(--muted)}.btn-nav{background:none;border:1px solid var(--border);padding:5px 14px;border-radius:var(--radius-sm);cursor:pointer;transition:all .15s}.btn-nav:hover{border-color:var(--blue);color:var(--blue)}.btn{display:inline-flex;align-items:center;justify-content:center;padding:10px 22px;border-radius:var(--radius-sm);font-size:14px;font-weight:500;cursor:pointer;border:none;transition:all .15s;text-decoration:none}.btn-primary{background:var(--blue);color:#fff}.btn-primary:hover{background:#3a7de8;text-decoration:none}.btn-ghost{background:transparent;border:1px solid var(--border);color:var(--text)}.btn-ghost:hover{border-color:var(--blue);color:var(--blue);text-decoration:none}.btn-sm{padding:6px 14px;font-size:13px}.btn:disabled{opacity:.4;cursor:not-allowed}.card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:24px}.card-sm{padding:16px}.form-group{display:flex;flex-direction:column;gap:6px;margin-bottom:18px}.form-label{font-size:13px;color:var(--muted);font-weight:500}.form-input{background:var(--bg);border:1px solid var(--border);color:var(--text);padding:10px 14px;border-radius:var(--radius-sm);font-size:14px;outline:none;transition:border-color .15s}.form-input:focus{border-color:var(--blue)}.form-error{font-size:12px;color:var(--red);margin-top:4px}.badge{display:inline-flex;align-items:center;padding:2px 10px;border-radius:20px;font-size:12px;font-weight:500}.badge-blue{background:var(--blue-dim);color:var(--blue)}.badge-green{background:var(--green-dim);color:var(--green)}.badge-amber{background:var(--amber-dim);color:var(--amber)}.badge-red{background:var(--red-dim);color:var(--red)}.progress-bar{background:var(--surface2);border-radius:4px;height:6px;overflow:hidden}.progress-fill{height:100%;background:var(--blue);border-radius:4px;transition:width .3s}.lecture-list{display:flex;flex-direction:column;gap:12px}.lecture-item{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:18px 20px;display:flex;align-items:center;gap:16px;cursor:pointer;transition:border-color .15s;text-decoration:none;color:var(--text)}.lecture-item:hover{border-color:var(--blue);text-decoration:none}.lecture-item.active{border-color:var(--blue);background:var(--blue-dim)}.lecture-num{width:36px;height:36px;background:var(--surface2);border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:14px;font-weight:600;color:var(--muted);flex-shrink:0}.lecture-num.done{background:var(--green-dim);color:var(--green)}.lecture-info{flex:1 1}.lecture-title{font-size:15px;font-weight:500}.lecture-meta{font-size:12px;color:var(--muted);margin-top:2px}.player-wrap{width:100%;aspect-ratio:16/9;background:#000;border-radius:var(--radius);overflow:hidden;position:relative}.player-wrap video{width:100%;height:100%}.player-watermark{position:absolute;bottom:12%;right:3%;color:hsla(0,0%,100%,.15);font-size:12px;font-family:monospace;pointer-events:none;-webkit-user-select:none;-moz-user-select:none;user-select:none}.quiz-wrap{margin-top:32px}.quiz-title{font-size:18px;font-weight:600;margin-bottom:20px}.question-card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:22px;margin-bottom:16px}.question-text{font-size:15px;font-weight:500;margin-bottom:16px}.options{display:flex;flex-direction:column;gap:8px}.option{display:flex;align-items:flex-start;gap:12px;padding:12px 16px;border-radius:var(--radius-sm);border:1px solid var(--border);cursor:pointer;transition:all .15s;-webkit-user-select:none;-moz-user-select:none;user-select:none}.option.selected,.option:hover{border-color:var(--blue)}.option.selected{background:var(--blue-dim)}.option.correct{border-color:var(--green);background:var(--green-dim)}.option.wrong{border-color:var(--red);background:var(--red-dim)}.option-letter{width:24px;height:24px;border-radius:50%;background:var(--surface2);display:flex;align-items:center;justify-content:center;font-size:12px;font-weight:600;color:var(--muted);flex-shrink:0}.option.selected .option-letter{background:var(--blue);color:#fff}.option.correct .option-letter{background:var(--green);color:#fff}.option.wrong .option-letter{background:var(--red);color:#fff}.explanation{margin-top:12px;padding:10px 14px;background:var(--surface2);border-radius:var(--radius-sm);font-size:13px;color:var(--muted);line-height:1.6}.score-card{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:32px;text-align:center;margin-top:24px}.score-number{font-size:56px;font-weight:700;line-height:1}.score-label{font-size:15px;color:var(--muted);margin-top:6px}.hero{padding:64px 0 48px;text-align:center}.hero h1{font-size:36px;font-weight:700;line-height:1.2;margin-bottom:16px}.hero h1 span{color:var(--blue)}.hero p{font-size:16px;color:var(--muted);max-width:480px;margin:0 auto 32px}.divider{border:none;border-top:1px solid var(--border);margin:32px 0}.flex{display:flex}.items-center{align-items:center}.justify-between{justify-content:space-between}.gap-8{gap:8px}.gap-12{gap:12px}.gap-16{gap:16px}.mt-8{margin-top:8px}.mt-16{margin-top:16px}.mt-24{margin-top:24px}.mt-32{margin-top:32px}.mb-8{margin-bottom:8px}.mb-16{margin-bottom:16px}.mb-24{margin-bottom:24px}.text-muted{color:var(--muted)}.text-sm{font-size:13px}.font-semibold{font-weight:600}.text-center{text-align:center}