CSS Units

Measurements

Unit	Description
%	percentage
in	inch
cm	centimeter
mm	millimeter
em	1em is equal to the current font size. 2em means 2 times the size of the current font. E.g., if an element is displayed with a font of 12 pt, then ‘2em’ is 24 pt. The ‘em’ is a very useful unit in CSS, since it can adapt automatically to the font that the reader uses
ex	one ex is the x-height of a font (x-height is usually about half the font-size)
pt	point (1 pt is the same as 1/72 inch)
pc	pica (1 pc is the same as 12 points)
px	pixels (a dot on the computer screen)

Colors

Unit	Description
color_name	A color name (e.g. red)
rgb(x,x,x)	An RGB value (e.g. rgb(255,0,0))
rgb(x%, x%, x%)	An RGB percentage value (e.g. rgb(100%,0%,0%))
#rrggbb	A HEX number (e.g. #ff0000)

use absolure size in,cm,mm only for printing.

use em,ex for block elements which contain text.

use px for layout.