body {
    font-family: Arial, sans-serif;
    background: #f4f4f4;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}
.container {
    background: white;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}
input {
    width: 200px;
    padding: 10px;
}
button {
    padding: 10px;
    background: green;
    color: white;
    border: none;
    cursor: pointer;
}
ul {
    list-style: none;
    padding: 0;
}
li {
    display: flex;
    justify-content: space-between;
    background: #ddd;
    padding: 10px;
    margin-top: 5px;
}
.completed {
    text-decoration: line-through;
    color: gray;
}