Here's the conflicting rule: https://github.com/alphagov/whitehall/blob/master/app/assets/stylesheets/frontend/views/_html-publications.scss#L174

!important flags are evil, but I think just occasionally their use is valid.  In this case, Footnotes are conceptually generic govspeak, but should have a consistent style regardless of format.  HTML attachments on publications have some specific styling rules for lists and paragraphs which also affect the footnote block, so in this case the generic styling rule overriding the specific rule is the desired outcome.

An other way to fix this would be to add a post-parse filter to the govspeak gem to pull out footnotes from the govspeak contents, but this wouldn't be ideal either since the footnotes are part of the document's contents.