The header, colmask and footer divs are 100% wide and stacked vertically one after the other. Colmid is inside colmask and colleft is inside colmid. The three column content divs (col1, col2 & col3) are inside colleft. Notice that the main content column (col1) comes before the other columns.
body {
margin:0;
padding:0;
border:0; /* This removes the border around the viewport in old versions of IE */
width:100%;
background:#fff;
min-width:600px; /* Minimum width of layout - remove line if not required */
}