body {
    font-family: Arial, sans-serif;
    margin: 20px;
    padding: 20px;
    background-color: #f4f4f4;
}

input[type="number"], button {
    padding: 10px;
    margin: 5px;
}

.hidden {
    display: none;
}

#error {
    color: red;
    margin-top: 20px;
}

#result {
    margin-top: 20px;
}