Custom Header Support

I want to add a custom background to my custom header/logo. (only Hueman choice is a custom color). I read other Support threads on topic and there seems to be a way to do this using CSS codes. Unfortunately, I’m not a programmer. It seemed easier for me to just create a new header logo with the custom background already there. I’ve done that, and uploaded it. Now I can’t seem to get it to center and fill the header area. I installed the Simple Custom CSS pluggin, copied and pasted the suggested command, but it is not displaying properly. Please advise. http://www.visionaryentrepreneurship.com