Allows you to change how the browser calculates the width of an element, that is, whether or not to include padding, borders, and margins, in the width or height calculation.
Extra padding does not make this box wider or taller. It will be only as large as its
height properties define.
IE8+, Chrome 10+, Safari 5.1+, Opera 9.5+
Firefox 2+, Chrome 4 - 9, Safari 3.1 - 5.0