Arc-theme, a beautiful, flat theme with transparent elements for GTK 3 and GTK 2 based desktop environments like Gnome, Unity, Budgie, Pantheon, etc.
Arc-theme is a new theme project still under development. It’s available is in three variants:
Full preview in Ubuntu Unity with Numix circle icons:
If you like the theme, try it by installing the .deb package available in the link below:
Needs Ubuntu 15.04 (higher), or Elementary OS Freya because it depends on GTK 3.14 / 3.16.
Once installed, apply the themes via Unity Tweak Tool (or System Settings -> Tweaks).