Delete hover color in menu

Hi folks!

I’m trying to remove the white hover color in the menu in this site i’m building.
http://tamaco.webbea.dk/ The password is tamaco

I have tried to find the right selector in firefox web developer tool and i get this selector:
.nav > li > a:focus, .nav > li > a:hover

So when i put in this code in my theme-css
.nav > li > a:focus, .nav > li > a:hover {background-color : none;} the white background color is still there! Can anybody see what I am doing wrong here?