resizing fonts with ems

[Deborah]

typical example page = http://www.lll.hawaii.edu/index.php/...ion-resources/

Aloha!

I learned just enough about css to be a hazard to myself, I fear. Hoping to be able to easily experiment with relative font sizes, I changed all font size designations from #px to #em except the one for textarea which I designated as 11px.

My thinking was that I could control all from there. Now I am unable to relatively enlarge (ever-so-slightly) the font size site-wide as per my elderly colleagues' requests.
I have tried to locate the solution via FireBug, but FireBug remains a major mystery in my life.

So, can anyone help? Also, any suggestions for a FireBug tutorial falls in the range between "for-dummies" and "for-geniuses" appreciated!