Hello,

Take this code:

body .product-label.attribute-label:not(.label-with-img) {
    background-color: rgba(255, 255, 255, 1);
    color: #000000;
    width: 100px;
    font-size: 20px;
}

Set the values you need, delete lines you do not need. Add this code to the Theme Settings > Custom CSS > type device you need.

Best Regards