Please see my comment to the question. It's possible that you don't understand the whole idea of CSS. This is nothing more than the
declarative language used to describe styles. You may need to get the idea of declarative languages:
http://en.wikipedia.org/wiki/Declarative_programming[
^].
Even though some declarative language may describe something like "commands", nothing like that happens with CSS. When the browser loads some HTML file, it loads all the CSS code, no matter if it is all embedded in that HTML or separate files (resources) are referenced. It's important to understand that
it happens only once. The style properties read from CSS are put in HTML DOM which ultimately defines the rendering of HTML. One can access DOM via Javascript and modify it. There is nothing dynamic in the CSS code written in HTML or CSS files; it remains fixed. When you dynamically modify, add, remove or replace styles of an HTML element, you do it to DOM; and all those changes immediately change the rendering of the page.
Please see:
http://en.wikipedia.org/wiki/Document_Object_Model[
^],
http://www.w3schools.com/js/js_htmldom_css.asp[
^] (you can find very basic explanation of changing styles here).
—SA
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