You have in the head of your HTML
and an external file in a location that is determined by the href=" ... " portion, the above example points to a stylesheet called site.css in the same directory as the HTML page that has called it.
<link rel="stylesheet" type="text/css" href="site.css" />
Your stylesheet is a file named by what you want to refer to it by and has the extension .css but in reality the extension could be anything you like but more relevent to keep use of the .css extension because editors and software that is used for production of web sites know then that its a stylesheet.
Unlice CSS in the HTML page, your stylesheet does not need the HTML tags for stylesheets.
Please remember to wrap any code you have in forum tags:-
[CODE]...[/CODE] [HTML]...[/HTML] [PHP]...[/PHP]
If you can't think outside the box, you will be trapped forever with no escape...