Centering Advanced Search Bar

Greetings-
A Two Part Question:

1) CENTERING: I am trying to customize my Search Bar by Centering it on a page. I have added Padding via Custom CSS, but that just causes alignment issues. Is there a simple way to center? I would like to use the ShortCode to add the Search Bar throughout the site.

http://girlsguidetoneworleans.com.routing.wpmanagedhost.com/sample-geo/

2) WIDTH: Even when I adjust the Search Fields via Custom CSS, they are still not 100% the same size. For example, when I have everything as 250px, the Search button appears more 275px. Any ideas?

Thanks so much!