lh

1lh is the used line height of the element. With line-height: 1.5 on a 20px font that comes to 30px, so block-size: 3lh holds exactly three lines of that text and min-block-size: 4lh makes a note panel at least four lines tall. The unit lets you size things in lines instead of guessing at pixels.

margin-block: 1lh gives paragraph spacing of exactly one blank line, in whatever font and size the paragraph uses. If line-height is normal, 1lh is the height of one line in that font, which differs from font to font, so set a number when you need the same result everywhere.

Inside the line-height property an element cannot refer to its own value, so lh there reads the parent’s. A child with line-height: 2lh under a parent whose lines are 20px tall gets 40px. And lh is a length, not a promise about the rendered text: a tall inline box, such as an 80px inline-block, stretches its line, so three lines with one such box in them are taller than 3lh.