So, on Android there's no issue as screen real estate is small. But on Windows I use a 24" 16:9 monitor. I like to maximise Diarium so it's the focus, but then the text in an entry runs all the way across the width of the screen and is difficult to read. If the padding could be adjusted to something like the attached picture, it would be a more pleasant experience.
Scrivener writing software has a full-screen focus mode where you can adjust the text width and background colour/opacity. There is also a free app called Focuswriter which allows you to do something similar. It might be worth having a look at these to get ideas.