Scoped themes to apply only to the editor (#editor-holder)

https://github.com/adobe/brackets/issues/8415
https://github.com/adobe/brackets/issues/8420
Just to clear up my own confusion... :-)  Why is the `theme.className` prefix needed?  I think in another thread you mentioned you're deleting the `<style>` tag when a theme is turned off... so is there any need to have a class placed on the root of the DOM if that class will always be present when the theme's rules are in memory?