body{font-family:sans-serif;max-width:600px;margin:2rem auto;padding:0 1rem}form{display:flex;gap:.5rem;margin-bottom:1rem}input[type=text],input:not([type]){flex:1;padding:.4rem}ul{list-style:none;padding:0}li{display:flex;align-items:center;gap:.5rem;padding:.4rem 0;border-bottom:1px solid #eee}li span{flex:1}.done{text-decoration:line-through;color:#999}.error{color:red}