Is there a good reason why we're defining global custom properties on :root/html and not on body?

@matuzo from memory when I saw this pop up a while back, essentially –

someone wrote it like that in the spec and here we are.

@sturobson I know that root {} is different depending on the context. In a document its <html>, inside an svg it's <svg>. It makes sense to just use :root everywhere for consistency. I was just wondering if there's a good reason against using body instead.
@matuzo @sturobson maybe it’s sort of ‘window’ as in the thing that contains the html or svg or plain-text or other