Black box on top

Hi, I would like to replace the black box on top with a graphic of the same size. How would I do that and what size would the graphic have to be?

http://avisualadvantage.net/SoldItClosedIt/2013/06/15/average-30-year-mortgage-rate-nears-4/

Thanks

 

Hello,

Paste this code in Custom CSS
Appearance > Theme Option > Styling Option > Custom CSS

Code:

.header_container.not_home {
 
background: url(your image address);
 
background-size: 100%;}