How to change navigation bar font?

Use Firebug to track it down, it is perfect for things like this. Will tell you the style sheet and line number you need to alter.

Does anyone know the style.css code to change the nav. font though?

Yes, like I said use Firebug. I found the style you need to change in the master.css file in just a few seconds.

We actually just posted a video tutorial on our site on getting started with Firebug to track down your WordPress CSS:

https://www.presscoders.com/editing-wordpress-theme-css-firebug/

Okay, thank you.