A dark theme with a beautiful blue-green schema for GtkSourceView based text editors.
Copy the chameleon.xml file into a folder of the style search path.
Typical search paths for GtkSourceView version 3.0:
~/.local/share/gtksourceview-3.0/styles//usr/share/gnome/gtksourceview-3.0/styles//usr/local/share/gtksourceview-3.0/styles//usr/share/gtksourceview-3.0/styles/
Typical search paths for GtkSourceView version 4:
~/.local/share/gtksourceview-4/styles//usr/share/gnome/gtksourceview-4/styles//usr/local/share/gtksourceview-4/styles//usr/share/gtksourceview-4/styles/
Select 'Chameleon' from Preferences -> Font's and Colors