.car-calc {
    max-width: 400px;
    margin: 1em auto;
}
.car-calc input,
.car-calc select {
    width: 100%;
    padding: 0.5em;
    margin-bottom: 1em;
    font: inherit;
}
.car-calc button {
    padding: 0.5em 1em;
    cursor: pointer;
}
#car-calc-result {
    margin-top: 1em;
    font-weight: bold;
}