Margin width is the transparent space around an element. It can be specified using absolute or relative units.
Relative units calculate the margin width using the width of the element's containing block .
Negative values for margin widths can be used. You can enter one to four values to set different widths for different margins of an element. If there is one value, all four margins are the same width. If there are two values, the first value sets the top and bottom margins, and the second value sets the left and right margins. If there are three values, the first value sets the top margin, the second sets the left and right margins, and the third sets the bottom margin.