# Install soft fork
sudo add-apt-repository ppa:fossfreedom/arc-gtk-theme-daily
sudo apt-get update
sudo apt-get install arc-theme

# Set it as the current theme
gsettings set org.gnome.metacity theme "Arc-Dark"
gsettings set org.gnome.desktop.interface gtk-theme 'Arc-Dark'
gsettings set org.gnome.desktop.wm.preferences theme 'Arc-Dark'