The new menu for style editing on a live article and world is great and I love it.
However it has a small issue, with worlds that use a custom CSS theme.   The issue can be summarized as such: if a custom theme is already loaded on the page, the theme selector only changes the header image in the preview, without affecting the css of the page, even if the custom css is removed first.   This may have something to do with the option "Load default stylesheet", which I had disabled, but enabling it in live preview doesn't solve the issue.   To get the editor to work, I had to:

1. remove the custom CSS
2. enable Load default stylesheet
3. save the changes and reload