This tutorial will show you how to install Arc Theme on Elementary OS Loki. Arc is a flat theme with a subtle color scheme and transparency in select parts of the window, like GTK Header Bars and the Nautilus sidebar. Arc supports most Linux distribution such as Debian, Arch, Ubuntu and Fedora. Since Elementary OS Loki is based on Ubuntu 16.04, we can easily install Arc Theme on Elementary OS Loki.
Here is the look of my Desktop with Arc Theme installed on Elementary OS Loki
How to install Arc Theme on Elementary OS Loki
Step 1. Install Elementary Tweaks
Please follow the steps on my previous post to install Elementary Tweaks on Loki. Elementary Tweaks is needed to change theme and icons and some other settings on Elementary OS.
Step 2. Install Arc Theme
Open Terminal and paste the following lines
sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04/ /' > /etc/apt/sources.list.d/arc-theme.list"
sudo apt-get update
sudo apt-get install arc-theme
Step 3. Apply Arc Theme
Open System Settings and open Tweaks. Select Arc Theme from the GTK theme list.