Relative units vs pixel value for font sizes

[sjwilczynski]

Hey folks, recently a new person in our team asked why we are not using relative font sizes in one of M365 controls. My initial answer was: "Because we do same thing as fluentui/react-components does and they use pixel values". But then I started wondering what's the real underlying reason and honestly I had no good answer. I checked out some articles (e.g The Surprising Truth About Pixels and Accessibility: should I use pixels or rems? (joshwcomeau.com)) and it seems there are some cases (and font size seems to be one of them), when relative units are recommended for accessibility. So why Fluent 9 uses pixel values for font size? Could you share some argumentation for that?

Looking forward to hearing from you!

cc @jurokapsiar, @layershifter, @levithomason I am tagging you as @Markionium said you might have some insights :)