How can I remove the white rectangle from my product quantity selector?

[JIZO]

Hello, I've been two hours trying to remove the white rectangle that appears in my quantity selector on the product page, but it has been impossible for me. I've tried a lot of CSS changes and nothing works.

The initial goal was to achieve something that looked like the selector in the picture below, but right now I'd be more than happy if I get to delete the white rectangle, leaving the rest as it is.

Thank you!

[Guleria]

Please share the store URL 

[JIZO]

https://4e3bd8.myshopify.com/products/copia-de-join-the-movement-white-oversized-t-shirt

I have changed the background of the element to make it the same color as the background, but the problem comes when I try to round the borders, it blends with a black border that I cannot remove and it looks weird.

Otherwise, is it possible to make it look like the one in the picture of the original message? I have worked previously with Webflow and I’m new to Shopify.

Thank you!