Ambiance dark theme is a modified version of the original Ambiance GTK3 theme by Ubuntu. Ambiance Dark theme includes color modifications and new metacity theme. Check how to install it and further information down bellow.
Ambiance Dark Theme modified by DLKreations Deviantart user.
Download Ambiance Dark Theme and further information.
[How To]: Install Ambiance Dark Theme
Run Terminal “Ctrl+Alt+t”, then type
sudo mv "theme directory" /usr/share/themes
Replace the the theme file name with the Ambiance dark theme zip file and theme directory as well without using the quotes.