:root{--bg:#0f172a;--bg-card:#1e293b;--bg-hover:#334155;--text:#e2e8f0;--text-muted:#94a3b8;--accent:#fbbf24;--easy:#10b981;--medium:#f59e0b;--hard:#ef4444;--border:#334155}*{box-sizing:border-box;margin:0;padding:0}body{background:var(--bg);color:var(--text);font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,sans-serif;line-height:1.6}a{color:var(--accent);text-decoration:none}.home-page{max-width:900px;margin:0 auto;padding:40px 24px}.home-header{text-align:center;margin-bottom:48px}.home-header h1{margin-bottom:8px;font-size:2.5rem}.home-subtitle{color:var(--text-muted);font-size:1.1rem}.home-progress{color:var(--accent);margin-top:8px;font-size:.9rem}.category-section{margin-bottom:36px}.category-title{color:var(--text-muted);border-bottom:1px solid var(--border);margin-bottom:16px;padding-bottom:8px;font-size:1.2rem}.problem-grid{grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:12px;display:grid}.problem-card{background:var(--bg-card);border:1px solid var(--border);border-radius:8px;padding:16px;transition:background .2s,border-color .2s;display:block}.problem-card:hover{background:var(--bg-hover);border-color:var(--accent)}.problem-card-disabled{opacity:.4;cursor:default}.problem-card-disabled:hover{background:var(--bg-card);border-color:var(--border)}.problem-card-header{justify-content:space-between;align-items:center;margin-bottom:8px;display:flex}.problem-card-header .problem-title{color:var(--text);font-weight:600}.problem-count{color:var(--text-muted);font-size:.85rem}.difficulty-badge{text-transform:uppercase;border-radius:999px;padding:2px 8px;font-size:.75rem;font-weight:600}.difficulty-easy{background:var(--easy);color:#fff}.difficulty-medium{background:var(--medium);color:#fff}.difficulty-hard{background:var(--hard);color:#fff}.problem-page{flex-direction:column;height:100vh;display:flex;overflow:hidden}.problem-header{border-bottom:1px solid var(--border);background:var(--bg);z-index:10;align-items:center;gap:24px;padding:16px 24px;display:flex}.back-link{color:var(--text-muted);font-size:.9rem}.back-link:hover{color:var(--accent)}.problem-content{flex:1;padding:24px;overflow-y:auto}.problem-description{color:var(--text);margin-bottom:24px;line-height:1.7}.problem-description code{background:var(--bg-card);border-radius:4px;padding:2px 6px;font-size:.9em}.problem-description pre{background:var(--bg-card);border:1px solid var(--border);border-radius:6px;margin:12px 0;padding:12px 16px;font-size:.9em;line-height:1.5;overflow-x:auto}.problem-description pre code{background:0 0;padding:0}.problem-description p{margin:8px 0}.problem-layout{grid-template-columns:1fr 1fr;gap:24px;min-height:400px;display:grid}.code-column{flex-direction:column;gap:16px;display:flex}.visual-column{flex-direction:column;display:flex}.code-panel{background:#0d1117;border-radius:8px;max-height:400px;position:relative;overflow:auto}.code-panel pre{padding:16px;font-size:14px;line-height:1.6}.code-panel code{font-family:JetBrains Mono,Fira Code,monospace}.visual-panel-wrapper{background:var(--bg-card);border-radius:8px;flex-direction:column;gap:16px;padding:16px;display:flex}.visual-panel{background:#1e293b;border-radius:6px;padding:12px}.visual-label{text-transform:uppercase;letter-spacing:.05em;color:var(--text-muted);margin-bottom:8px;font-size:.75rem}.variables-panel{background:var(--bg-card);border-radius:8px;padding:12px 16px}.panel-title{text-transform:uppercase;letter-spacing:.05em;color:var(--text-muted);margin-bottom:8px;font-size:.75rem}.panel-empty{height:120px;color:var(--text-muted);background:var(--bg-card);border-radius:8px;justify-content:center;align-items:center;display:flex}.step-narration{background:var(--bg-card);border-top:1px solid var(--border);border-bottom:1px solid var(--border);text-align:center;color:var(--accent);padding:12px 24px;font-size:.95rem}.kbd-hint{color:var(--text-muted);white-space:nowrap;margin-left:12px;font-family:monospace;font-size:.75rem}.step-controls{background:var(--bg);border-top:1px solid var(--border);justify-content:center;align-items:center;gap:8px;padding:12px 24px;display:flex}.ctrl-btn{background:var(--bg-card);border:1px solid var(--border);color:var(--text);cursor:pointer;border-radius:6px;padding:6px 12px;font-size:16px;transition:background .2s}.ctrl-btn:hover{background:var(--bg-hover)}.ctrl-btn-play{background:var(--accent);color:#000;border-color:var(--accent)}.ctrl-btn-play:hover{opacity:.9}.step-scrubber{appearance:none;background:var(--border);cursor:pointer;border-radius:2px;outline:none;width:120px;height:4px}.step-scrubber::-webkit-slider-thumb{appearance:none;background:var(--accent);cursor:pointer;border-radius:50%;width:14px;height:14px}.step-counter{color:var(--text-muted);margin:0 12px;font-family:monospace;font-size:14px}.speed-selector{gap:4px;display:flex}.speed-btn{border:1px solid var(--border);color:var(--text-muted);cursor:pointer;background:0 0;border-radius:4px;padding:2px 8px;font-size:12px;transition:all .2s}.speed-btn:hover{border-color:var(--accent);color:var(--accent)}.speed-btn-active{background:var(--accent);color:#000;border-color:var(--accent)}.problem-category{color:var(--text-muted);margin-left:8px;font-size:.8rem}@media (width<=768px){.problem-layout{grid-template-columns:1fr}}