em - font size of the parent element
rem font size of the root element
em is a good candidate for adding padding to typographic elements. That way, when the font-size of the text grows, the padding/spacing between components grows also.
Both ch and ex pertain to the (approximate) width and height of one character respectively.
ch is equal to the width of a 0
ex is equal to the height of a x
ch is helpful for restricting max-widths for readability. [[20210201144247-line-length]]
[[20220104103715-viewport-units]]