I just had to change to another device, from my laptop, in order to make the "accept" button visible on a custom terms of service popup. Any click outside the popup dismissed it so scrolling didn't work to gain access to the button.

The screen in question is 768 vertical resolution, so not too unusual, and there was a lot of unnecessary vertical white space on the popup that pushed the button off screen.
Browser was Chrome on windows.

Simply making this popup less high, or moving the button away from the lower corner, would enable a much better sign up experience.

Alternatively remove the behavior that dismisses the popup when attempting to scroll.