Do you combine CSS and SSI for basic site structure?

I'm a CSS and PHP newb - just starting to convert over from tables and ASP. In my ASP sites, I would create a header and footer file containing the main site layout and use SSI so I could quickly and easily alter design and elements common to all pages of my site (i.e. nav bar, top/bottom links, etc.).

Do you only use CSS to control site layout and edit your CSS file to make site-wide changes or do you also use SSI? I'm thinking there isn't a way to do it all through CSS if you want to be able to edit a nav bar, for instance, from a single place to update your entire site.

This is the way I'm imagining a common page structure would need to be... (I don't know PHP syntax yet so just bear with the header and footer locations)

header.php

<div id="content">blah blah blah</div>

footer.php

Code (markup):

 

I build the page in html and css, then cut the html up into header, navigation, footer, and the content. I call the header, navigation, and footer in the content file using a php includes.

 

Thanks, that confirms what I was thinking.