Customize the "Add to cart" pop-up screen (Not the Mini-Shoppingcart)

Question:
![Customize AddtoCart popup.PNG|690x273]
Does anyone know how/where to make edits to this screen?

Product:
Wix Editor

What are you trying to achieve:
We are currently setting up a webshop, and added a few products to our page.
When pressing the “Add to Cart” button, it gives you a pop-up window in which you can select the size and color of the item, before it gets added to your cart in the Mini-Shoppingcart window on the right.

I simply want to either get the text to be Black, or the background to be Black, so the text is legible.
I have looked through all the editable webpages, all the Text Theme’s, but nowhere can we edit this pop-up.