Background images do not dictate the size of the container they are applied to..
You should always start by explaining what you are trying to do.
If what you want is a texture behind the Site title and tagline that does not scale down when the browser gets smaller, and make that area 232px, then remove your rule, and instead, put the rule below in Main Options > Header > Site Title / Tagline > Title / Tagline Area BG CSS+ box
IF this is not what you are trying to do, please elaborate.