fastah, a very easy way indeed is available.
Firstly, do you know how to use element inspect by Firefox, or some other element inspection application?
if you do not, let me know.
If you do know how to use it, find the font area you want to manipulate, then copy past the code into your Custom CSS at admin/themes control panel under customization tab. Or tiki-admin.php?page=look#contentadmin_look-5
if your code is good, it will over ride your theme css files. It's best to modify your themes via Custom CSS over rides, because if you modify the actual theme files, when you upgrade your Tiki, your theme mods will be lost.