*{box-sizing:border-box;margin:0;padding:0}body{font-family:-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,sans-serif;background:#f5f5f5;min-height:100vh}.container{max-width:500px;margin:0 auto;padding:40px 20px}h1{text-align:center;margin-bottom:30px;color:#333}.auth-form,.todo-form{display:flex;flex-direction:column;gap:12px;margin-bottom:20px}input{padding:12px;border:1px solid #ddd;border-radius:6px;font-size:16px}button{padding:12px 20px;background:#4a90d9;color:#fff;border:none;border-radius:6px;cursor:pointer;font-size:16px}button:hover{background:#357abd}.btn-secondary{background:#6c757d}.btn-danger{background:#dc3545;padding:6px 12px}.header{display:flex;justify-content:space-between;align-items:center;margin-bottom:20px}.todo-list{list-style:none}.todo-item{display:flex;align-items:center;gap:12px;padding:15px;background:#fff;border-radius:8px;margin-bottom:10px;box-shadow:0 1px 3px #0000001a}.todo-item.completed span{text-decoration:line-through;color:#999}.todo-item span{flex:1}.toggle-link{color:#4a90d9;cursor:pointer;text-align:center;margin-top:15px}.error{color:#dc3545;text-align:center;margin-bottom:10px}