Help make header background gradiant

Hello, I am playing with the free download to see how to make changes and edits for a site I would like to build. one area I am having a hard time finding a solution is to make the header image area background a gradiant color.
I would like the full width to be a repeating gradiant and then I would like to put a png logo over the gradiant as a header image.
Can someone more knowledgeable with this theme and css please provide some help?

Thank you in advance.

The page I need help with: [log in to see the link]