"Paper" size in Compose Mode

When I’m in Compose Mode, the “paper” doesn’t reach to the top or bottom of the screen the way it used to. Now there is wide black space at the top and bottom margin roughly the size of my dock and the menu and format bars (even a little larger). I’d like to use the entire screen real estate. It used to look different, so I assume I’ve somehow hit some preference that I didn’t intend. I hope this makes sense. Any help? Thanks!

In Composition mode, move your cursor to the foot of the screen. An overlay appears. On the left hand side of the overlay is a slider that controls ‘paper’ width. Press the Alt key and the slider switches to paper height. (A usage I find valuable: if you want to control the urge to edit while writing, reduce the height to give a ‘letterbox’ view.)

That was it! Thank you very much