CSS Library: Horizontal CSS Menus: Here
CSS3 Semi Opaque Menu
Author: Dynamic Drive
Linear gradient backgrounds in CSS3 lets you add a graduating background to any element on the page. It's supported in FF3.6, Safari 2+ and Google Chrome. In IE9 (which currently doesn't support CSS3 Linear Gradients), SVG is used to create a similar look while IE gets its act together. With that said, this menu takes advantage of CSS3 gradient background to produce a menu with a semi opaque rollover effect. Whatever the solid background color of the main UL behind it, the menu item's background peeks through. Peek-a-boo!