Presentation mode: Can't see the whole block

In the presentation mode, blocks larger than the .reveal window get cropped, and there doesn’t seem to be a way for desktop users to scroll it down to see the rest of the content.

Changing .reveal's overflow to scroll in the custom CSS does enable vertical scrolling, but the window would instantly snap back to the top of the block.

I can change the app’s font size with - and + to shrink the blocks, but the scaling feels slow and rough.