This is a replacement GUI for the original Counter Strike Source.
In addition to the cool image you get a list of all TWKgaming.com servers for you to connect at the distance of a mouse click.
Download the file in the link below then extract the content of the cstrike folder in the zip file to your cstrike folder:
The correct path should be C:\Steam\steamapps\(your user)\counter-strike source\cstrike if your steam installation is on the C: drive
The correct path for the files after extracting should be:
\Steam\steamapps\(your user)\counter-strike source\cstrike\materials\console\background01.vtf and background01_widescreen.vtf
\Steam\steamapps\(your user)\counter-strike source\cstrike\resource\GameMenu.res
To uninstall the GUI just remove the files listed above.
For those that have the old version just overwrite the files.