Yes, Production site using the Theme CLI ( which I guess is one of its downsides, despite its otherwise it’s a great workflow?)
That makes total sense.
Yes, with plugins it’s my goto but with TCs there’s a good temptation to dev against a Production site because of the immediacy of feedback (if not always very helpful!)
But I’ve just realised, you can enter localhost with the CLI and it works.
So duh!
I will use that going forward! 
I have no idea why I thought that wouldn’t be possible 
As usual, thanks for your help that’s saved me a lot of time (in the future 
)