This example demonstrates a bug in webkit browsers. If you zoom the page out, you will see that at certain zoom levels the width of the box will get reported as "554px" instead of "555px" as is set in the CSS. This can cause obvious problems for some layouts at different zoom levels where exact pixels dimensions are required.

.box {
	width: 555px;  
	height: 400px; 
	background: #ccc; 
	margin: 0 auto; 
	color: #000; 
	padding: 20px; 
	line-height: 150%; 
}

Use "⌘ +" and "⌘ -" to zoom in and out.