CSS for selected item in menus

This is not how it normally works. For CSS, the notion of "selection" is insignificant. To implement highlighting, you should handle some events of the DOM elements using JavaScript. In the event handler, you modify the style class of the element when it changes the state (for example, please see documentation on .addClass and .removeClass below). The most convenient way of doing it I know is jQuery.

Please see these CSS methods:
http://api.jquery.com/addClass/[^],
http://api.jquery.com/addClass/[^],
http://api.jquery.com/toggleClass/[^],
http://api.jquery.com/category/css/[^].

If you need to learn jQuery (I highly recommend it), please see:
http://en.wikipedia.org/wiki/JQuery[^],
http://docs.jquery.com/Tutorials:How_jQuery_Works[^],
http://docs.jquery.com/Tutorials[^].

—SA