Try viewing this page with and without CSS stylesheets. You can easily do this in Firefox using the View > Page Style > No Style menu item. Without styles, it just ordinary text. With styles, you see a "cool" banner image.
You can define this banner style in an external stylesheet, so that it will apply to all of your pages. That way, you don't have to insert the banner code in each page.
This coding technique is due to http://csszengarden.com/, which is a very cool site.