How to change font size in sidebar?

I'm wondering how to change the size of the sidebar text (the actual content text, not the header text size). I'd like it to be 80% of the size of the body text, so it doesn't compete with the body as much.

ETA: If I insert font-size:80%; into the #left-column and #right-column sections of the CSS file, it also makes the sidebar's contents fill only 80% of the sidebar's space, for some reason. See here:

http://www.safemotherhoodproject.org

Thanks!