The default css does not set a font so users will see whatever they have defined in their chosen browser.
I have told you how to edit the css in another thread. For this one you go to your heading styles, paragraph styles and anything else and go to the font dropdown. There you define the font name, size, colour and whatever. Stick to basic fonts that users will have on a standard installation machine. There are ways of making non standard fonts work but get this working first.
Then your users will see what you want them to see, albeit the browser will allow them an override but most people don't use that.
Please use the Blue reply button at the top to help me help you. The black Reply link nests replies and they sort out of order.