body {
    font-family: Arial, sans-serif;
    background-color: #f0f0f0;
    text-align: center;
}

.container {
    margin-top: 100px;
}

#box {
    width: 100px;
    height: 100px;
    background-color: #3498db;
    margin: 20px auto;
    cursor: pointer;
}

.hidden {
    display: none;
}

.red {
    background-color: #e74c3c;
}