How To: Change the Font Size of the Username in Postbit
 

To change the size of the username in the postbit, edit the additional.css template:

Admin CP -> Styles & Templates -> Style Manager -> Edit Templates -> CSS Templates -> additional.css

And add this:

Code:
.postbitlegacy .userinfo a.username, .eventbit .userinfo a.username {
font-size: XXpx;
}
...with XX being the font size.