The dark theme for Ubuntu 14.04 or later.
First of all, make sure you have installed Unity Tweak Tool:
sudo apt-get install unity-tweak-toolAfter that, for install theme to your system open a terminal and use the following commands:
git clone https://github.com/mervick/Ambiance-Darkness.git
sudo mv -f Ambiance-Darkness /usr/share/themes/Ambiance-DarknessStart Unity Tweak Tool. Go to Unity Dash and search for Unity Tweak tool:
You’ll find the Theme option in the Appearance section.
Once you have selected the Themes option, you will find all the themes present in the system here. Just click on the "Ambiance Darkness". It will be changed instantly.
