Arkham GTK Theme
Arkham (?), formerly known as adwaita-atom, is another dark theme for GTK3 and GTK2. It's directly generated out of the Adwaita gresources that are shipped with GTK to provide an easily maintainable theme that always works for the latest GTK versions. Basically it's a darker variant of Adwaita with a black menubar. The dark gradients are similar to the ones that are used in the Base16 Tomorrow Dark Atom theme.
(Awesome-WM with Atom, Caja and Mate-Terminal)
(Mate-Desktop with Atom, Caja and Eye-of-Mate)