That's a header Stephen put together (thanks Stephen!).
To answer your question, the light theme is plain and simple where as the dark theme has more to it (borders, tables, other images, etc.) so copying/pasting it wouldn't work.
I'll send Stephen a PM and see if he can do anything with the dark theme.
For those wondering how to quickly change themes do this (old picture, same concept):
To save it to your account (so every time you login you're automatically on that theme), go to:
http://www.fordrangerforum.com/profi...do=editoptions
Scroll down to the bottom and select the 'forum skin' you would like to save as your default.