Hi Margaret
Indeed you may add a Font button to the .CHM viewer.
Unfortunately, RoboHelp doesn't expose a method to do it easily.
You would have to do it by compiling using Microsoft HTML Help
Workshop.
Here is a link to a page explaining it.
Click
here and read all about it
I'm not sure if CSS font sizes will override this or not.
Additionally, you may wish to try pressing and holding the Alt key
while rolling the mouse wheel (if you have one) as this sometimes
changes the font.
Cheers... Rick