adds a checkered background to images, so images with transparency are revealed.
based upon: http://lea.verou.me/css3patterns/#checkerboard
img {
background-color: #FEFEFE;
background-image: -webkit-linear-gradient(45deg, #CBCBCB 25%, transparent 25%, transparent 75%, #CBCBCB 75%, #CBCBCB), -webkit-linear-gradient(45deg, #CBCBCB 25%, transparent 25%, transparent 75%, #CBCBCB 75%, #CBCBCB);
background-image: -moz-linear-gradient(45deg, #CBCBCB 25%, transparent 25%, transparent 75%, #CBCBCB 75%, #CBCBCB), -moz-linear-gradient(45deg, #CBCBCB 25%, transparent 25%, transparent 75%, #CBCBCB 75%, #CBCBCB);
background-image: -o-linear-gradient(45deg, #CBCBCB 25%, transparent 25%, transparent 75%, #CBCBCB 75%, #CBCBCB), -o-linear-gradient(45deg, #CBCBCB 25%, transparent 25%, transparent 75%, #CBCBCB 75%, #CBCBCB);
background-image: -ms-linear-gradient(45deg, #CBCBCB 25%, transparent 25%, transparent 75%, #CBCBCB 75%, #CBCBCB), -ms-linear-gradient(45deg, #CBCBCB 25%, transparent 25%, transparent 75%, #CBCBCB 75%, #CBCBCB);
background-image: linear-gradient(45deg, #CBCBCB 25%, transparent 25%, transparent 75%, #CBCBCB 75%, #CBCBCB), linear-gradient(45deg, #CBCBCB 25%, transparent 25%, transparent 75%, #CBCBCB 75%, #CBCBCB);
-webkit-background-size: 30px 30px;
-moz-background-size: 30px 30px;
background-size: 30px 30px;
background-position: 0 0, 15px 15px;
}