JSFiddle : http://jsfiddle.net/LutJQ/9/
Solution without rotate
header:before {
z-index: -1;
position: absolute;
content: '';
left: 0px;
bottom: -10px;
width: 0;
height: 0;
border-top: 10px solid transparent;
border-bottom: 10px solid transparent;
border-right:10px solid #476473;
}