Double scrollbars @ Signup Popup

The popup shows double scrollbars, in every major browser, as shown in this Firefox screenshot.

The issue comes from the CSS rule “overflow: hidden” being ignored when the popup with the iframe appears, since “.gh-portal-popup-wrapper” has an “overflow: scroll” rule.

Since this is inside an iframe, the css can’t be updated in any way. Do someone knows a way to replace the overflow: scroll with overflow: hidden (or even auto) ?

My mom told me to go to law school. That there will be days like today. Why I did not listen.