Heya,
I think this Forum has automatically reformatted the quotation marks (a.k.a. inverted commas) from the link in my original post, to the curved style, which doesn’t work, so the
“ ”
around the URL, should be
" "
By that I mean it needs to be parallel quotation marks, like this:
"https://raw.githubusercontent.com/easaw/ThinkDark/master/ThinkDark.css"
Hope that helps anyone, as it can be a problem when copying links like this from the web.
(oh, and I meant to say, I know it’s not your fault Darren! 
)