Font classes not applied consistently

[micw]

Hello,

I tried to switch to a sans-serif font, so I added

params:
  body_classes: "sans-serif"
  post_content_classes: "sans-serif"

That works in most places but not everywhere.

On the article overview, the caption is still serif:

Same for the caption in post details:

[regisphilibert]

Closed in favor of #573