Edit product variant boxes on Mobile view

Site URL: https://www.mulberrypaperco.com/cambridge-collection/p/invitation-set

Hello, 

I'd like to edit the product variant boxes on the mobile view so that they extend across the screen. Also I'd like to edit the add to cart "customize" button to do the same thing as well. However, I am worried that editing them on the mobile view will affect the display of the desktop view as well. Any suggestions or custom code? Thank you!!

Add to Design > Custom CSS

/* Mobile-Variant */
@media screen and (max-width:767px) {
.ProductItem-details .product-variants {
    width: 100%;
}
}