body {
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    background-color: #f4f4f4;
}

header {
    background: #35424a;
    color: #ffffff;
    padding: 10px 0;
    text-align: center;
}

main {
    padding: 20px;
}

form {
    margin: 20px 0;
}

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

button {
    padding: 10px;
    background: #35424a;
    color: #ffffff;
    border: none;
    cursor: pointer;
}

#result {
    margin-top: 20px;
    font-size: 1.2em;
}