Header Background

Hi there, I've been trying to get the background of the header (see http://www.wowow.eu) set to transparent. So far, I used "#masthead {background-color: transparent;}" and guess what... it didn't work :(( When I use a different color (i.e. #f41414) it works well. I also like to get the background of the header-menu-margins (set to top=25px; bottom=15px) transparent... Nothing worked out so far :( Can you help? Thanks in advance... Cheers, Steve