Do you mean a background color/image for your blogs?

For color: <*style>.node{background-color:black}<*/style>

Replace "black" with the color of your choice, or with a color code (such as #0B2C42).

For an image: <*style>.node{background-image:url('http://example');}<*/style>

Replace "http://example" with the url of the image you want to use.


Take out the "*" in the code to use it, and remember to put any CSS under the cut.
Hope that helps, please ask if you need more help or clarification.