After you do the child theme as WPyogi suggested the style that you are going to want to change is the
background-color: rgb(122, 33, 33);
that will change the white background box that the content sits on, if you want to change the background color behind the content, that can be done via the admin interface:
Appearance -> Background
Appearance -> Customize link -> Colors, and you can play with a few options there with color pickers and everything very easily.
@codeman1234: As per the Forum Welcome, please post your own topic. Posting in an existing topic prevents us from being able to track issues by topic. Added to which, your problem – despite any similarity in symptoms – is likely to be completely different.