Plata is a new Gtk+ theme based on the latest Material Design refresh. The theme comes in 3 variants, regular (mixed), Lumiere (light) and Noir (dark), each with regular and compact versions.
The theme, which mixes black, indigo and grey with bits of red and purple, supports Gtk+ 3.20.x, 3.22.x and 3.24.x, as well as Gtk+ 2, and a multitude of desktop environments like Gnome Shell (and Flashback), Cinnamon, Xfce, Mate, LXDE, and Budgie Desktop.