This is some custom css that changes the way tweetdeck looks.
From the old dark theme (https://www.dropbox.com/s/27s5ck421jiz50r/Screenshot%202014-04-09%2015.08.09.png) to this
To install on mac right click on the tweet deck app then click show package contents and navigate to /Contents/Resources/htdocs/web/css/ and then open the app-dark.(some string).css file. Add the css code above to the bottom of this file and make sure that the tweetdeck theme is set to dark. Other platforms will follow soon.
This is still a work in progress but if you have any ideas or questions just tweet me @code_cookies.