body {
    background-color: #111;
    color: #eee;
    font-family: Arial, sans-serif;
}

h1 {
    color: #fff;
}

form {
    margin: 20px;
}

input[type="number"], input[type="submit"] {
    background-color: #333;
    border: 1px solid #555;
    color: #eee;
    padding: 8px;
    border-radius: 4px;
    margin-bottom: 10px;
}

input[type="submit"] {
    cursor: pointer;
}

input[type="number"]:focus, input[type="submit"]:focus {
    outline: none;
}

#result {
    margin: 20px;
    font-size: 18px;
}