The surprising truth about pixels and accessibility

Should web developers use pixels or ems/rems for accessible fonts?

It’s an emotionally-charged question because there are a lot of conflicting opinions out there, and it can be overwhelming. Maybe you’ve heard that rems are better for accessibility. Or maybe you’ve heard that the problem is fixed and pixels are fine?

The truth is, if you want to build the most-accessible product possible, you need to use both pixels and ems/rems. It’s not an either/or situation. There are circumstances where rems are more accessible, and other circumstances where pixels are more accessible.
↫ Joshua Comeau

The linked article isn’t just an explanation of why, but also a tutorial.