Suburbia theme – transperncy

Hello,

In this theme’s header there’s a grey horizontal strip that I’d like to make transparent so the cool background would be seen under it. I know how to change its color, but is it possible to make it transparent?

That’s the original code:
.header { height: 50px; border-bottom: 15px solid #E0E0E0; padding: 15px; position: relative; }

And this is my site: http://infectzia.net/frank/

Thanks!