Shrink right margin in Text body

In my document I can type normally, but there is a huge right margin, when I write some text. See here:

That can be only be amended if I heavily zoom in. Is there some way to shrink that right margin to a normal size?

This is probably related to CSS that doesn’t originate with ProseMirror.

+1 this shall not be related to PM. Just fire up chrome devtools and inspect the elements to see which the right margin comes from.