:root{--bg:#222538;--bg2:#2c3047;--bg3:#373c56;--bg4:#434969;--surface:#31364e;--border:#a855f740;--border-focus:#3b82f699;--primary:#8b5cf6;--primary-hover:#7c3aed;--accent:#f97316;--accent-hover:#ea580c;--green:#10b981;--red:#f43f5e;--yellow:#f59e0b;--purple:#a855f7;--text:#fff;--text-muted:#e2e8f0;--text-dim:#cbd5e1;--font-sans:"Inter", system-ui, -apple-system, sans-serif;--font-mono:"Space Mono", "Fira Code", monospace;--radius:12px;--shadow-sm:0 1px 2px 0 #00000026;--shadow-md:0 4px 6px -1px #0003, 0 2px 4px -1px #00000026;--shadow-lg:0 10px 15px -3px #0000004d, 0 4px 6px -2px #00000026;--glass:#222538bf;--glass-border:#a855f726}*{box-sizing:border-box;margin:0;padding:0}body{background-color:var(--bg);color:var(--text);font-family:var(--font-sans);-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale;line-height:1.5;overflow-x:hidden}body:before{content:"";z-index:-1;pointer-events:none;background:radial-gradient(circle,#8b5cf614 0%,#0000 70%);width:50%;height:50%;position:fixed;top:-10%;right:-10%}body:after{content:"";z-index:-1;pointer-events:none;background:radial-gradient(circle,#3b82f614 0%,#0000 70%);width:50%;height:50%;position:fixed;bottom:-10%;left:-10%}h1,h2,h3,h4,h5,h6{letter-spacing:-.025em;font-weight:700}button{cursor:pointer;background:0 0;border:none;font-family:inherit;transition:all .2s cubic-bezier(.4,0,.2,1)}input,textarea{background:var(--bg3);border:1px solid var(--border);color:var(--text);border-radius:var(--radius);outline:none;padding:10px 14px;font-family:inherit;transition:border-color .2s}input:focus,textarea:focus{border-color:var(--primary)}.glass{background:var(--glass);-webkit-backdrop-filter:blur(12px);border:1px solid var(--glass-border)}.btn{border-radius:var(--radius);justify-content:center;align-items:center;gap:8px;padding:10px 20px;font-size:.95rem;font-weight:600;display:inline-flex}.btn-primary{background:var(--primary);color:#fff;box-shadow:0 4px 12px #8b5cf64d}.btn-primary:hover{background:var(--primary-hover);transform:translateY(-1px);box-shadow:0 6px 16px #8b5cf666}.btn-secondary{background:var(--bg3);color:var(--text);border:1px solid var(--border)}.btn-secondary:hover{background:var(--bg4);border-color:var(--text-dim)}.card{background:var(--bg2);border:1px solid var(--border);border-radius:var(--radius);padding:20px;transition:transform .2s,box-shadow .2s}.card:hover{box-shadow:var(--shadow-md);border-color:#a855f74d}@keyframes fadeIn{0%{opacity:0;transform:translateY(10px)}to{opacity:1;transform:translateY(0)}}.fade-in{animation:.4s ease-out forwards fadeIn}::-webkit-scrollbar{width:8px;height:8px}::-webkit-scrollbar-track{background:var(--bg)}::-webkit-scrollbar-thumb{background:var(--bg3);border-radius:4px}::-webkit-scrollbar-thumb:hover{background:var(--bg4)}.challenge-overlay{-webkit-backdrop-filter:blur(8px);backdrop-filter:blur(8px);z-index:1000;background:#222538e6;place-items:center;padding:20px;display:grid;position:fixed;inset:0}.challenge-card{border:1px solid var(--glass-border);text-align:center;border-radius:24px;width:100%;max-width:500px;padding:40px}.challenge-card h3{color:var(--text);margin-bottom:24px;font-size:1.5rem}.question-text{color:var(--text-muted);margin-bottom:32px;font-size:1.1rem;line-height:1.5}.options-grid{gap:12px;margin-bottom:32px;display:grid}.option-btn{background:var(--bg3);border:1px solid var(--border);color:var(--text);text-align:left;border-radius:12px;padding:14px 20px;font-weight:500;transition:all .2s}.option-btn:hover:not(:disabled){background:var(--bg4);border-color:var(--primary)}.option-btn.selected{border-color:var(--primary);color:var(--primary);background:#8b5cf626}.challenge-actions{gap:12px;display:flex}.result-text{border-radius:8px;margin-bottom:24px;padding:12px;font-weight:600}.result-text.success{color:var(--green);background:#10b98126}.result-text.error{color:var(--red);background:#f43f5e26}.completion-success{color:var(--text);background:#f973161a;border:1px solid #f9731633;border-radius:16px;align-items:center;gap:16px;padding:24px;display:flex}.completion-success h4{color:var(--accent);margin-bottom:4px}.btn-accent{background:var(--accent);color:#fff;box-shadow:0 4px 12px #f973164d}.btn-accent:hover{background:var(--accent-hover);transform:translateY(-1px)}.badge-success{color:var(--green);background:#10b98126;border:1px solid #10b9814d;border-radius:20px;padding:4px 10px;font-size:.75rem;font-weight:700}.nav-actions{gap:12px;display:flex}.completion-card{background:#f9731614;border:1px solid #f9731633;border-radius:20px;justify-content:space-between;align-items:center;gap:20px;padding:30px;display:flex}.completion-info{align-items:center;gap:20px;display:flex}.completion-info h4{color:var(--accent);margin-bottom:4px;font-size:1.2rem}.completion-info p{color:var(--text-muted)}.next-lesson-btn{white-space:nowrap;padding:12px 24px}.ai-feedback-box{background:var(--bg3);border:1px solid var(--border);text-align:left;border-radius:16px;margin-bottom:24px;padding:24px}.ai-feedback-box.correct{border-color:#10b98166}.ai-feedback-box.wrong{border-color:#f43f5e66}.status-icon{margin-bottom:16px}.status-icon.success{color:var(--green)}.status-icon.error{color:var(--accent)}.feedback-text{color:var(--text);font-size:.95rem;line-height:1.6}.flex-1{flex:1}