After I posted the above I was thinking about my suggestion of using the body versus html tag for styling and when I made the post my reasoning was that you don't (can't?) put text between the html and /html tags. What does go between them are the head and body tags, see the w3c page
https://tinyurl.com/y2lew3je.
Given that lots of people use styling attached to the html tag I'll assume that the css does propagate down to the body tag.
Then I started thinking about that propagation and if it could be useful and I remembered the footer tag and was thinking that perhaps it goes after the body tag, within the html tag. Nope, the footer tag goes within the body tags. So I stand by what I said about it making more sense to use the styling on the body tag.
Although now I'm wondering what happens if you use styling on the html tag (at the bottom of the last css file) in an effort to mitigate objectionable styling used by the author, e.g., if they put theirs on the body tag.
I would like to come up with a minimal recipe for repairing objectionable styling, and have the recipe work on all books. But I'm hot getting my hopes up for that last part.
Edit:
I've struck out lots of malarky because I was confused about margins being inherited, but they're not. Although I still think it makes better sense to set the margin on the body and not the html.