The New Contributor dialog is masked from where the comment section ends.
Here are some screenshots just to be more clear:
Fixed by Aaron: Question's first two line and the upvote arrow are clamped
The root cause here was a different change made to temporarily prevent scrolling at small screen sizes. The root cause of the scrolling was the new Share pop-up. With that identified (albeit not yet fixed), the temporary fix can be removed (and a small pile of related bugs completed).