BuddyPress.org

No, not the buddypress css, your Theme’s Style.CSS.

The easiest way to access this is in the wordpress admin –> Go down to the theme editor, and go down to the bottom to your style.css.

Now find this piece of css:

`/* Main Content

#content {
width:960px;
margin: 0px auto;`

right below the last line, add
`background-color: #85C8F2;`