If you mean the small areas between the widgets, then if you go into Edit Site > Edit Styles > (select the style) > Color Theme and then pick your colour theme, you can customise it. Once you get into the customisation options, you can choose transparencies .. I think the one you're probably looking for is "content underlay" (you may need to untick the "generate colors" button).
Alternatively, one or two of the supplied "templates" doesn't have that gap at all. You could try the Pawn template?
I have been trying many different CSS lines in an attempt to have the black bars that should be covered with widgets disappear.
Is it possible to make the background transparent? (I am new to CSS and might just be doing things wrong)
Thank you in advance.
This is the site for reference: http://crux.gamerlaunch.com/?gid=550222