Why not simply posting the error message verbatim? Again, verbose prose doesn’t tell the same as concise code (or error message, as here).
Because the message depends on the browser. I always try multiple browsers because of all the compatibility issues. Chrome, for example, gives me an error specifically saying “Not allowed to load local resource: file:///Users/john/Library/CloudStorage/Dropbox/Miscellaneous/Prism/prism-vs.css” when I use the @import directive (which I don’t think is any clearer than what I said), but other browsers give slightly different versions of the error.
Well, one can search engine with that (a lot better than with prose). And immediately finds this:
So, the solution might be to store the CSS somewhere in the DT web server’s document hierarchy. I do not have that product, so I don’t know how/where that would be. With a standard web server on macOS, I’d use /Users/<me>/Sites/....
Yeah, I still think your claim fails as I can also search for what I said (“Not allowed to load local resource”) and find exactly the same article you mentioned and others. More detail does not always mean more clear. Regardless, fiddling around guessing how to get the web server to work with the @import directive isn’t worth any more time now that I’ve just smashed everything together into a single CSS file. Maybe some other soul with more copious free time than I possess can pick up that ball and run with it.