Is it possible to override this payment processor's modal "script blocking" function to inject my own custom CSS?

this payment processor's modal has in-line css that takes priority over all other css on the page no matter what (I don't wanna list out all the absurd stuff I tried, but no combination of classes and !important could this to work without js)--I even got on a zoom call for half an hour with a developer that works for the payment processor, because he was sure he would be able to do it, but he just couldn't.

Here is an example (my site is not live so I cannot link to mine). https://www.landify.design/templates/bruno This is not an example of the "too tall" modal that I mention down below, just fyi. this is just a normal sized one but with the same behavior and permissions, to show what I'm talking about. Just click the Download template button to trigger the modal.

The modal's in-line css overwrites everything, and then there is something in the modal's behavior that prevents any kind of JS tomfoolery after the iframe has loaded (which makes sense for security reasons, and I understand why they do that).

But I got confirmation from the dev that if I'm able to find a way to modify the css, I'm not breaking any of their TOS. I just wanna condense the modal down to fit on basically any laptop that might open it--right now it's just like nearly 2 screens tall and it looks kind of silly.

Anyways, I know it's a long shot, but I was hoping there was maybe some kind of trick to inject CSS successfully with a script after this div has loaded. I made a script that executes properly after the modal appears, but it only affects elements outside of the iframe, no matter what I try. Any tips or advice? I realize this is probably impossible but just have to ask.

Note: Probably doesn't matter, but my site is built on Laravel.

Thank you!