ex unitThe ex CSS length unit is a font-relative length equal to the used x-height of the first available font. X-height is often equal to the height of the lowercase x.unitsUnitswidely2015-07-292018-01-29https://drafts.csswg.org/css-values-4/#font-relative-lengthshttps://developer.mozilla.org/docs/Web/CSS/Reference/Values/lengthcss.types.length.exhttps://nowyoucanuse.com/features--ex.html