rem
Widely available since 2018-01-29
The rem CSS length unit is a font-relative length that is equal to the font size of the root HTML element which for most browsers is 16px.
Learning resources on MDN
Browser support (view on caniuse.com)
- Chrome 4 Released on 2010-01-25
- Chrome Android 18 Released on 2012-06-27
- Edge 12 Released on 2015-07-29
- Firefox 3.6 Released on 2010-01-21
- Firefox for Android 4 Released on 2011-03-29
- Safari 5 Released on 2010-06-07
- Safari on iOS 4 Released on 2010-06-21