Topic on Project:Support desk

I'm just wondering how one would go about editing the CSS of the topmost portion of the wiki - the one where you see your log-in info as well as the buttons to edit the page. I'm asking since in my current wiki, the plain white clashes with the background, especially since it happens right behind the logo. I figure it can be edited with Common.css, but for the life of me, I can't figure out the syntax.

http://omniversenexus.net/wiki/Main_Page

How can I change the white to something else, say a gradient, or even just hide it altogether to show more of the background?

*MediaWiki version: 1.28.2

*PHP version: 5.6.30 

If necessary, here's the link to the CSS page: http://omniversenexus.net/wiki/MediaWiki:Common.css

EDIT: Here's an example of what I'm talking about:

http://zelda.gamepedia.com/Main_Page

This wiki edited the top header to be blue and smoothly transition in to the rest of the background.

To find div ids for particular elements in webpages, you can make use of browser developer tools. In Chrome pressing Ctrl + Shift + C will open a selection feature then you can select any element on the webpage which will open its id and properties.

The div id for the top navbar is: p-personal. To hide it you can use:

#p-personal { display: none; }

Thanks. I should be on the right track now. Just have to play around more.