This GTK theme matches My chocolate theme for Compiz with Emerald. As far as I know it uses the crux engine. It blends perfectly with the chocolate theme for Emerald that can be seen in the screen shot.
Just extract the downloaded file to the .themes folder in your home directory then choose Chocolate from Your GTK settings panel. Please make sure there is no other theme named Chocolate in the .themes directory before extracting or You will overwrite it.
This should work with any Linux that puts user added themes in the .themes folder in the home directory.
Like Gentoo, Sabayon, and others.