body {
    font-family: 'Arial', sans-serif;
    background-color: #f8f8f8;
    margin: 0;
    padding: 0;
}

header {
    background-color: #333333;
    color: #ffffff;
    text-align: center;
    padding: 1em 0;
}

#calculator {
    max-width: 400px;
    margin: 20px auto;
    background-color: #ffffff;
    padding: 30px;
    border-radius: 10px;
    box-shadow: 0 0 20px rgba(0, 0, 0, 0.1);
}

label {
    display: block;
    margin-bottom: 10px;
    color: #333333;
}

select,
input {
    width: 100%;
    padding: 12px;
    margin-bottom: 20px;
    box-sizing: border-box;
    border: 1px solid #cccccc;
    border-radius: 5px;
}

button {
    background-color: #333333;
    color: #ffffff;
    padding: 12px;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    width: 100%;
    font-size: 16px;
}

button:hover {
    background-color: #555555;
}

#result {
    margin-top: 20px;
    font-weight: bold;
    font-size: 18px;
    color: #333333;
}