I've been doing the html and css for a site, sending it off to a guy to implement in a web server. I get a call from the designer freaking out about the progress, saying the clients aren't happy. He wants me to personally integrate my css with what's on the site. The site is done in ASP.net, time is short, and I'm a little in over my head. I have an understanding of how php works, but have never worked extensively with it.
Looking at the stuff on the ftp, I can't even find equivalent of the index.html file (I know that when I go to the site itself, there is nothing after the base url, i.e., www.site.com/ brings me to the homepage.)

Can anyone give me a few tips or links as to what I am to do with this, or where to even being navigating this site?