a unique characteristic of the line-height property: it is the only CSS property for which non-zero numeric values are allowed without units.
The line-height property isn’t alone in this respect: z-index, flex-grow, flex-shrink and many other properties all support numeric values without units.
The
line-height
property isn’t alone in this respect:z-index
,flex-grow
,flex-shrink
and many other properties all support numeric values without units.Also,
line-height: 0
is valid in CSS.