Josh Collinsworth avatar Josh Collinsworth

Why you should never use px to set font-size in CSS

Screenshot of “Why you should never use px to set font-size in CSS”

Let’s be very clear: it absolutely does matter what unit you use in your CSS. And you should avoid px when setting font-size wherever possible.

I'm amazed we still have to say this, 9 years after I gave a whole 50 minutes talk about the em unit (rem was young): Un petit pas pour l’em, un grand pas pour le Web.

How can some front-end developers still ignore that users DO change font size?

I however understand why most don't know that the default font size in browsers is not always 16px, as this is really rare (Josh even writes "On the web, the default font size is 16px" 🤷‍♂️), but users setting a preferred default and/or minimum font size is not so rare. I use text-only zoom in Firefox really often.

It's also revealing that people don't remember what one em originally represented. Josh writes "Em originally referred to the width of an “M” character", but it was originally actually more related to the height of the character.