Understanding Demo CSS?

Understanding Demo CSS?

I'm working with the Accordian widget with ASP.NET MVC 2. I know how to use CSS in ASP.NET Web Forms, unsure about JQuery css. 
 
The projects default stylesheet can be found here :
<link href="../../Content/Site.css" rel="stylesheet" type="text/css" />

The JQuery UI demo stylesheet (including Accordian css) can be found here:
<link rel="stylesheet" href="../../Content/themes/base/jquery-ui.css"/>
 
Here is the Accordian header code:
<script type="text/javascript" >
$(function () {
$(
"#accordion").accordion({
collapsible:
true }); });
</script>
 
Q. Where is the #accordian reference found in the jquery-ui.css?  
Q. What if I have accordians on different pages and need different css for each?
Q. Is it possible to use 'sub .css' links (references) in the main site .css?