Ummm.... Then change it.
Open Carbonites options to the "Font" page and click on the font you want to change to get a list of fonts. Click on the font in the list that you want to use for that particular part of Carbonite (I believe it will only change the fonts for the various parts of Carbonite) and it will change to that font. You can change the font size by clicking on the "Size #" on the page.
If the font you would like to use is not in the list, I believe Carbonite will use
SharedMedia. At least, there are _a_lot_ of fonts in my Carbonite list that that's the only way I can figure they got there. If you're going to use the "SharedMedia" addon, I highly suggest you open the "SharedMedia" folder and look for the "INSTRUCTIONS for MyMedia" plain text file, and read through it. It will make adding media to your WoW much easier.