What is the best way to edit the payment gateway CSS?

[Jackster]

I am new to Prestashop and have a dark theme with multiple payment gateways.

We had this issue with Woo as well so looking for advise on the best way to make the checkout functional.

 

Here are some screenshots of the issues we are having with the dark theme.

 

The first screenshot is of the Stripe gateway. As you can see, the text in the credit card input is dark. 

The second is of the Klarna checkout and you can ignore the pink text but the rest is dark and the hyperlink text are near invisible.

The TOS check is also dark.

 

What is the best way to fix these issues? 

 

I see I can add custom CSS but when trying to modify, it does not update the website. I did clear cache and my browser does not cache. 

Thanks