Arc Theme - very beautiful flat design theme

Arc is a flat theme with transparent elements for GTK 3, GTK 2 and Gnome-Shell which supports GTK 3 and GTK 2 based desktop environments like Gnome, Unity, Budgie, Pantheon, XFCE, Mate, etc.

Installation latest version into Linux Mint 18:

sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04/ /' >> /etc/apt/sources.list.d/arc-theme.list"
cd /tmp; wget http://download.opensuse.org/repositories/home:Horst3180/xUbuntu_16.04/Release.key; sudo apt-key add - < Release.key
sudo apt update
sudo apt install arc-theme

Installation latest version into Linux Mint 17.3:

sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_15.10/ /' >> /etc/apt/sources.list.d/arc-theme.list"
cd /tmp; wget http://download.opensuse.org/repositories/home:Horst3180/xUbuntu_15.10/Release.key; sudo apt-key add - < Release.key
sudo apt update
sudo apt install arc-theme

Installation latest version into Linux Mint 18.1:

sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04/ /' > /etc/apt/sources.list.d/arc-theme.list"
cd /tmp; wget http://download.opensuse.org/repositories/home:/Horst3180/xUbuntu_16.04/Release.key; sudo apt-key add - < Release.key
sudo apt update
sudo apt install arc-theme

In the screenshot below I chose the option Arc-Darker

Good Luck!!!

https://github.com/horst3180/arc-theme