Consider dropping 'px' postfixing for numeric CSS properties

[kripod]

Motivation

After a discussion on a React issue and seeing where Preact 11 is steering:

adding px is definitely a historial feature that isn't as relevant these days. Folks should be opting to use relative units rather than static units (like px), otherwise they break their app/website to users who use zooming tools or accessibility tooling – invaliding Web Content Accessibility Guidelines.

I've seen it confuse new developers first-hand when switching between writing CSS and declaring inline styles.