OK, I understand the problem I was having with the Ctrl+Space.
You do not get full screen if you have selected the graph (you'll see
a little circle on each corner of the graph when you have done that).
If, for example, you tap in an empty box nearby, which unselects the
graph, Ctrl+Space will then work.

Customizing the font style or size is still a problem as the stylus can't
reach the controls. Any way to fix this?