body {
    background-color: #222;
    color: #fff;
    font-family: Arial, sans-serif;
    padding: 20px;
}
input[type="number"] {
    background-color: #333;
    border: none;
    border-radius: 5px;
    box-sizing: border-box;
    color: #fff;
    margin-bottom: 10px;
    padding: 10px;
    width: 100%;
}
input[type="number"]::placeholder {
    color: #999;
}
#output {
    color: #f0f0f0;
    cursor: pointer;
    margin-top: 10px;
}