#door-calculator {
    border: 1px solid #ddd;
    padding: 15px;
    background: #fafafa;
    border-radius: 8px;
    max-width: 650px;
}
#door-calculator h4 {
    margin-top: 15px;
}
#door-calculator label {
    display: block;
    margin-bottom: 8px;
}
.opening {
    border: 1px dashed #aaa;
    padding: 10px;
    margin-bottom: 10px;
    background: #fff;
}