In addition to the column widths, there are only two other classes defined: ‘column’ and ‘row’. The column class has a margin of 10 pixels applied to both the left and right edges, resulting in a cumulative 20 pixel gutter. Also note the ‘overflow: hidden’ attribute applied to both column and row. The real purpose of this technique is to clear floats, circumventing the need for a ‘clear: both’ declaration. Finally, we need to set the ‘display: inline’ property on ‘.column’ to prevent the double-margin bug in IE6.