Congratulations on v. 3.0.
Does the custom forum theme do anything if one uses the "light" forum colour scheme? I was unable to notice any difference.
It should still work on light, but all the text colours are a bit unreadable over the grey-blue background, so until I can explicitly set all the text colours it's supposed to show a little alert box suggesting you change to the dark theme for now. It looks like I must have made a change after testing that which stops it from working correctly. I'll send up a new version to fix it early next decade ;)