HV Menu v5.41 - transparent menus

[Bugle]

I have noticed on the authors site that the drop down menus under the example menu are transparent. Does anybody know how this is done?

http://www.burmees.nl/menu/menus.htm

[applesauce]

looking at his source code,

and then look at his js files (here's one: http://www.burmees.nl/menu/scripts/menumenu_var.js)

[Bugle]

Thank you