It's not the css - whatever they programed in previous and however they did it, that's the stuff you need to look at.
I have been given this assignment with the critical goal of not having the site be down at all.
You know on super large high traffic sites they also have a hard time meeting this goal? ;)
Standard procedure is to build a development site with the db and content from the production site. Then start making your changes.
These forums were CLOSED to new posts on November 19th, 2012. New forums are here: http://www.studiopress.com/forums/
and you will need to SIGN UP AGAIN.
If you need assitance with setting up your theme, go to http://my.studiopress.com/
and read the SETUP links or the TUTORIALS link on the side tab.
If you need Account Assistance
, file a help desk ticket at the same location.