Create contribution modal doesn't allow scrolling

[ceedubs]

The create contribution modal doesn't support scrolling. This is problematic if you are in a small browser window, since you can't see or get to the Submit contribution for review button.

I just ran into this on a 13" laptop with a browser window that wasn't quite maximized:

I tried doing a standard scroll (two finger swipe on the trackpad), but it didn't budge or indicate that there was more content below.