You can import it via the menus: language>define your language - select import and drill down to the .xml in the attached. I recommend backing up your current instance of NPP, just in case.
Themes are like, um, opinions (we all have them and they don't often appeal to the masses). So yeah, I have a gray background, with comments dimmed (a bit darker shade of gray), etc. The more important element is the work put into the language definition (keywords, folders, operators, etc.). It's all therein and customizable to our likings.
I offer it up, just in case it might be of use to someone else. Here is a pic of the UI (https://i.imgur.com/Ov6EtfI.png):

Enjoy.
-t