I can already see one conflict, which is the margin-top: one is in em, the other in rem.
My problem is wearing too many hats —*I might make a quick change on the fly and get distracted elsewhere, leaving such discrepancies in place.
Oh well, one step forward at a time...
(Not sure why I put the "display:block" in there. I may have swiped the css from one of my websites during early testing. At least I didn't put a "box-sizing" declaration in there...)