One value set: A padding value of 1em for all four sides.
Two values set: A padding value of 1em for the top and bottom, 2em for right and left.
Three values set: A padding value of 1em for the top, 2em for right and left, 3em for bottom.
Four values set: A padding value of 1em for the top, 2em for the right, 3em for the bottom, 4em for the left.