the double-quotes are not the expected double-quote characters.
Try cutting and pasting this instead: (you need to figure out how to get your keyboard to give you regular double quotes instead of the curly ones)
I was having the same error.
Maybe this is a bug on the site.
Finally I found that the closing bracket “}” on the previous CSS rule was missing.
Hopefully this is not a bug and it was our mistake deleting it accidentally.