I'd like to say I knew this and just forgot because I never use anything other than unitless, but this might just have been something I never knew 🤷

Kevin Powell

Unitless numbers and percentages for CSS line-height behave differently due to how inheritance works. When using a unitless value like 1.5, the line-height is recalculated on an element-by-element basis relative to each element's own font size. When using a percentage, the line-height is computed once on the parent element and then the resulting pixel value is inherited by all children — meaning smaller or larger text won't get proportionally adjusted line-height. Unitless values are generally the better choice for consistent, scalable typography.

Wait, line-height works like that?!

how different is unitless with em?
i’ve been using like 1.14em all my life like for a decade?
like all css tutorials out there uses em or unitless (forgot), never even heard about using % as line height ever since

This is why you should always hire a frontend specialist that knows a million of these small things rather than some all-around fullstack dev which can do 80% of the work but the other 20% will look like crap in many scenarios.
BTW this is known thing for decades. Always use unit-less values for <code>line-height</code> CSS property.

Love learning these little details!

I read something about this about two years ago and I’ve been using unitless line height ever since!