Adding Opacity to Page Menu & Drop-down Submenu

I'm new to building websites, but I love this theme!

I only have one issue: I want the drop-down page menu to have some opacity.

My page menu will drop-down vertically, but this (http://www.cssplay.co.uk/menus/flyout_horizontal.html) is a good example of what I'm trying to achieve.

Is this possible in Atahualpa?

Thanks!