Similarly to font-size we also have a large variety of line-height definitions, these are a mix of px, em, and unitless values.
It’s important to fix line-height here as well, because otherwise we’ll still have problems scaling font-size. For example, If you want to update a 14px (1em) font-size to 16px, and there’s a 14px line-height set, you now have a line-height that’s too small for your font-size.
That’s why it’s recommended that unitless line-height values are used, because your line-height will always be based on the font-size. With 14px font-size and line-height of 1, your line height will be 14px. Update the font-size to 16px and your line-height will be 16px. Unitless line-heights serve as multipliers of the font-size, not values.