CSS3 calc()

I have a dynamic width

Code used in this page

.calc {
	width: 100px;
	height: 100px;
	border: 1px solid #f00;
	padding: 10px;
	
	/* Firefox */
	width: -moz-calc(75% - 100px);
	/* WebKit */
	width: -webkit-calc(75% - 100px);
	/* Opera */
	width: -o-calc(75% - 100px);
	/* Standard */
	width: calc(75% - 100px);
}