gridmarket, make header image, span full width where default orange space is

in the gridmarket child theme be default there is a full page width orange row.

now i know i could upload a banner and all that good stuff, but what i want to do is have a full page width image spanning across the page right where the orange is, the banner would be custom tailored for height and have excess width with repeat property..

i already tried

#branding {background-image:url(;}

and #branding-wrapper but couldnt quite get it.