triangles.css

div:before {
    position: absolute;
    content: " ";
    display: block;
    left: 0;
    top: 0;
    border-right: 50px solid #fff;
    border-bottom: 50px solid transparent;
    width: 50% !important;
    height: 0;
    z-index: 9;
}
div:after{
	position: absolute;
    content: " ";
    display: block;
    right: 0;
    top: 0;
    border-left: 50px solid #fff;
    border-bottom: 50px solid transparent;
    width: 50% !important;
    height: 0;
    z-index: 9;
}