Changing body font size

This is so simple I can’t believe I’m coming up short. My brain must be fried.

I just want to change the font size for the main body of text and the post title sizes, if possible. The body text is priority, because the font I’ve chosen (Forum) is naturally small so I need the text size to default a little larger. Any ideas on a code to enter in the custom css or editor to make this happen? Right now I have the stylesheet completely set to the default.