Default System Font

Greetings all.
I am using ckeditor in a component for special needs kids.
The client wishes to have only serif fonts so the students can read them better.

I have disabled the font selector in the toolbar but the actual system font in the instance of ckeditor is using a sans-serif font.

How/where do I set that font to Times New Roman?

I have looked everywhere and all the support pages I have read discuss setting default fonts for the font selector...