There isn’t much theme development going on for latest Ubuntu release since it requires theme creator to build their theme from scratch for new GTK versions, it seems development almost went away but there are still people who are giving their free time just to make your desktop elegant, make sure to support them as well. Vimix GTK themes available in dark and light version and for GTK 3.20/3.22 there are more variants which means you get more themes on latest 16.10 desktop. It is a flat Material Design theme designed for GTK 3, GTK 2 and Gnome Shell based on Flat-Plat theme, and these themes are compatible with most of the desktop environments such as Unity, Gnome, Mate, Cinnamon, Xfce, Budgie and so on. If you find any kind of bug or issue within this theme then report it to creator via linked page. Shadow and Papirus icons used in the following screenshots. You can use Unity Tweak Tool, Gnome-tweak-tool.