*{margin:0;padding:0;box-sizing:border-box}:root{--bg-primary: #ffffff;--bg-secondary: #f8fafc;--text-primary: #1e293b;--text-secondary: #64748b;--border: #e2e8f0;--accent: #3b82f6;--accent-hover: #2563eb;--shadow: 0 1px 3px 0 rgb(0 0 0 / .1), 0 1px 2px -1px rgb(0 0 0 / .1);--shadow-lg: 0 10px 15px -3px rgb(0 0 0 / .1), 0 4px 6px -4px rgb(0 0 0 / .1);--radius: 8px;--transition: all .2s ease}[data-theme=dark]{--bg-primary: #0f172a;--bg-secondary: #1e293b;--text-primary: #f1f5f9;--text-secondary: #94a3b8;--border: #334155;--accent: #60a5fa;--accent-hover: #3b82f6;--shadow: 0 1px 3px 0 rgb(0 0 0 / .3), 0 1px 2px -1px rgb(0 0 0 / .3);--shadow-lg: 0 10px 15px -3px rgb(0 0 0 / .3), 0 4px 6px -4px rgb(0 0 0 / .3)}body{background:var(--bg-primary);color:var(--text-primary);font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,sans-serif;line-height:1.6;transition:var(--transition)}#app{min-height:100vh;display:flex;flex-direction:column;align-items:center;justify-content:center;padding:2rem;gap:2rem}.header{text-align:center;margin-bottom:1rem}.header h1{font-size:2.5rem;font-weight:700;color:var(--text-primary);margin-bottom:.5rem}.header p{color:var(--text-secondary);font-size:1.1rem}.theme-toggle{position:fixed;top:2rem;right:2rem;background:var(--bg-secondary);border:1px solid var(--border);border-radius:var(--radius);padding:.75rem;cursor:pointer;transition:var(--transition);box-shadow:var(--shadow)}.theme-toggle:hover{transform:translateY(-2px);box-shadow:var(--shadow-lg)}.input-container{display:flex;gap:1rem;width:100%;max-width:500px}input{flex:1;padding:1rem 1.5rem;border:1px solid var(--border);border-radius:var(--radius);background:var(--bg-secondary);color:var(--text-primary);font-size:1rem;transition:var(--transition);outline:none}input:focus{border-color:var(--accent);box-shadow:0 0 0 3px #3b82f61a}input::placeholder{color:var(--text-secondary)}button{padding:1rem 2rem;background:var(--accent);color:#fff;border:none;border-radius:var(--radius);font-size:1rem;font-weight:600;cursor:pointer;transition:var(--transition);white-space:nowrap}button:hover{background:var(--accent-hover);transform:translateY(-1px)}button:active{transform:translateY(0)}.todo-container{width:100%;max-width:600px}ul{display:flex;flex-direction:column;gap:.75rem;list-style:none}ul li{display:flex;align-items:center;gap:1rem;background:var(--bg-secondary);border:1px solid var(--border);border-radius:var(--radius);padding:1rem 1.5rem;cursor:pointer;transition:var(--transition);box-shadow:var(--shadow)}ul li:hover{transform:translateY(-1px);box-shadow:var(--shadow-lg)}ul li.completed{opacity:.7;background:var(--bg-primary)}ul li.completed span{text-decoration:line-through;color:var(--text-secondary)}.todo-checkbox{width:1.25rem;height:1.25rem;border:2px solid var(--border);border-radius:4px;display:flex;align-items:center;justify-content:center;transition:var(--transition);flex-shrink:0}.completed .todo-checkbox{background:var(--accent);border-color:var(--accent)}.completed .todo-checkbox:after{content:"✓";color:#fff;font-size:.875rem;font-weight:700}.todo-text{flex:1;font-size:1rem;color:var(--text-primary);transition:var(--transition)}@media (max-width: 640px){#app{padding:1rem;gap:1.5rem}.header h1{font-size:2rem}.theme-toggle{top:1rem;right:1rem;padding:.5rem}.input-container{flex-direction:column;gap:.75rem}button{padding:.875rem 1.5rem}ul li{padding:.875rem 1rem}}@media (max-width: 480px){.header h1{font-size:1.75rem}.header p{font-size:1rem}input,button{font-size:.875rem}}