<P> Although the size of the em ultimately depends on the point size, or height of the metal body of a letter, it is also used as a measure of horizontal spacing relative to the type size, with vertical spacing being measured in picas or points . One em was traditionally defined as the width of the capital M in the current typeface and point size, because the M was commonly cast the full - width of the square blocks, or em - quads (also mutton - quads), which are used in printing presses . </P> <P> In modern typefaces, the character M is usually somewhat less than one em wide . Moreover, as type includes a wider variety of languages and character sets than just those based on Latin, and needs a consistent way to refer to size, its meaning evolved long ago; this allowed it to include fonts, typefaces, and character sets which do not include a capital M, such as Chinese and Arabic . Because of how digital type works, the em now always means the point size of the font in question . </P> <P> In Cascading Style Sheets, the em unit is the height of the font in nominal points or inches . The actual, physical height of any given portion of the font depends on the user - defined DPI setting, current element font - size, and the particular font being used . </P> <P> To make style rules that depend only on the default font size, another unit was developed: the rem . The rem, or root em, is the font size of the root element of the document . Unlike the em, which may be different for each element, the rem is constant throughout the document . </P>

What is full form of em in css
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