Change design of buttons for product variants

Site URL: https://www.housefruits.com/store/be-yourself-sweatshirt

Hey.

We have tried to change the design of the buttons for the drop down of the product variants on all of our product pages. We wanted them to have the same white, half-round shape instead of the black square shape. Unfortunately the black shape is still there as some kind of overlay. Any idea on how to keep the white shape and get rid of the black shape? Or change the design of these buttons in general?

I attached a screenshot. Link to one of our product pages:

https://www.housefruits.com/store/be-yourself-sweatshirt

Password: Fruitfish5HoF

Any help would be much appreciated!