You should use values like rem, em and ch as they're related to font sizes. If your root font size is 16px then 1rem equals 16 px, you can set the line height t

You should use values like rem, em and ch as they're related to font sizes. If your root font size is 16px then 1rem equals 16 px, you can set the line height to 1.5rem etc. With ch you can limit how many characters an element should fit.