How to install Arc GTK Theme on ubuntu
Arc is a flat GTK theme with transparent elements for GTK 3, GTK 2 and Gnome-Shell. It is available in 3 variant Arc, Arc-Darker,Arc-dark. It supports GTK 3 and GTK 2 based desktop environments like Gnome, Unity, Budgie, Pantheon, XFCE, Mate, etc.
To install Arc GTK theme on ubuntu, you need to add theme authors’s personal repository. Open terminal and run the below command.
sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04/ /' >> /etc/apt/sources.list.d/arc-theme.list"
Then type your ubuntu password.
Then type the below command and hit enter,
sudo apt-get update && sudo apt-get install arc-theme
Confirm the installation by typing y. Then to install these packages without verification, type y and hit enter.
You can also add the repository key to apt.To add the key type the below command and hit enter.
sudo apt-key add - < Release.key
To apply the theme use Unity Tweak Tool.
To know more about this visit the arc theme homepage