I have tried setting the theme by specifying the theme attribute on the body but this does appear to work with the react components. Only way I can get it to work is by adding the css class. Can we get it documented how we should be doing this correctly? TBH I couldn't even see it documented on how to apply the theme when using standard, I got it from the youtube video below
https://youtu.be/R-J_xsYGRKg
Attached is a gif which shows the body attribute not working: