CSS is pt still a bad idea for screen and accessibility?

Question

So I'm reading using pt as a screen font size is bad as it's an absolute measurement and can render differently, but mostly these are old articles.

I've tried outputting text in 18pt/12pt/9pt alongside 1.5em/1em/0.7em and using various browsers' built in zoom capabilities the output adjusts consistently and similarly for both.

Additionally, when I'm reading the WCAG2 guidelines everything it says about font sizing is based on pt (e.g. 18pt for large text).

I guess the question is as the title, is pt really such a bad idea, and why and where does it fall over outside of my simple test?

thanks.

Answer 1

Advice against pt and other physical units is still valid from the accessibility point of view. The reason is that different people need different font sizes, and physical units fight against that, in the digital medium where font sizes would otherwise be adjustable.

It is true that all modern browsers have zooming capabilities, which work around some of the problems caused by physical units. But zooming is different from changing font size.

You can see this by testing with a page that sets some font size in pt and contains an image, too. When you zoom, all dimensions get changed. But when you change font size, using the browser controls for the purpose, IE 11 still refuses to adjust a size set in pt units. And this is, maybe arguably, correct behavior. And generally, when people want increased font size, they want just that—not zooming. Everything should work as otherwise, just with a larger size set for text. This works well when you, as an author, don’t set font size at all. If you set font size in pt, it doesn’t.