Dark GTK theme for Ubuntu 16.04 (Unity)

Arc Theme Dark

This seems to be a popular theme, albeit somewhat different from the original Unity. This theme also prefers cold colours producing an overall calming and comfortable desktop.

Update: After using this theme for a couple of weeks I must say this is the best I ever had with Unity. The choice and combination of colours is spot on, a serene and beautiful theme. Highly recommended.

This theme can be installed from the Nooblabs PPA:

sudo add-apt-repository ppa:noobslab/themes
sudo apt-get update
sudo apt-get install arc-theme

There is also an Arc icons theme, check more details at the NoobsLab webpage.

Adapta Dark

This theme introduces a number of modifications to window decorations and icons, but the end result is quite crisp. All the colours seem to have been well worked out, producing a nice desktop in different monitors.

Installation:

sudo apt-add-repository ppa:tista/adapta -y
sudo apt-get update
sudo apt-get install adapta-gtk-theme

It might require some tweaking to get activated, check the details here or follow the steps below.

Install unity-tweak-tool to apply the newly installed theme using:

sudo apt-get install unity-tweak-tool

Now navigate to unity-tweak-tool > Appearance > Theme to choose theme.

You can also try the Vivacious-zbackout theme.

Doesn't look great with Firefox. I'm trying to set different themes for GTK and Window theme to see if that helps, not working so far.

Details here: http://www.noobslab.com/2016/04/vivacious-colors-another-great-icon.html

Install commands:

sudo add-apt-repository ppa:ravefinity-project/ppa
sudo apt-get update
sudo apt-get install vivacious-colors
sudo apt-get install vivacious-folder-colors-addon
sudo apt-get install vivacious-colors-gtk-dark