I wrote about Arc GTK theme on this blog multiple times because it’s one of my favorite themes. It’s available in three color variants: light, dark, darker. I’m not the only one who really like this theme and the users were requesting the author to release it for Cinnamon and for web browsers like Chrome / Chromium or Firefox and also for Plank dock. The developer heard these voices and these versions are now available.
Arc GTK theme requires GTK 3.14 so it runs well on elementary OS and Ubuntu 15.04 (or later), but it won’t work on Ubuntu 14.04 or Linux Mint 17.x unfortunately.
If you’re wondering about how to install this theme on your distribution go to this page and select your distro. If you’re using elementary OS you should select Ubuntu and follow the instructions for Ubuntu 15.04. Installation instructions for Firefox, Chrome / Chromium and Plank can be found under the Extras section of the theme’s Github page.