body {
    font-family: Arial, sans-serif;
}

.container {
    width: 300px;
    margin: 0 auto;
    text-align: center;
}

input[type="number"] {
    margin: 10px 0;
    padding: 8px;
    width: 100%;
}

button {
    padding: 10px 20px;
    cursor: pointer;
}

#result {
    margin-top: 20px;
}

#prompt {
    color: red;
    font-size: 0.8em;
    margin-top: 10px;
}