Transparent Background in Header

Hi,

firstable I want to thank you for your great work, these theme is really good thinking ! Thanks guys !

However, i have one question : I try to change the background color of the header section into a transparent color (top bar include), but in the selector section on the Highend Options panel, it’s not possible to make a transparent color! A special code is possible in this selector, or can i do make this directly in the css code ?!
(sorry for my approximative english 😉 )