body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #f0f0f0;
}

.container {
    background: white;
    padding: 20px;
    border-radius: 5px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}

ul {
    list-style: none;
    padding: 0;
}

li {
    display: flex;
    justify-content: space-between;
    padding: 10px;
    border-bottom: 1px solid #ddd;
}

li.completed {
    text-decoration: line-through;
    color: #888;
}

button {
    background: none;
    border: none;
    cursor: pointer;
}