em unitThe em CSS length unit is a font-relative length equal to the specified font size. In an element with a 2 inch font, 1em equals 2 inches.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.emhttps://nowyoucanuse.com/features--em-unit.html