Black & white image to color image on hover

img{
-webkit-filter: grayscale(100%);
-webkit-transition-duration: 0.8s;
-moz-transition-duration: 0.8s;
-o-transition-duration: 0.8s;
-ms-transition-duration: 0.8s;
}

img:hover{
-webkit-filter: grayscale(0%);
-webkit-transition-duration: 0.8s;
-moz-transition-duration: 0.8s;
-o-transition-duration: 0.8s;
-ms-transition-duration: 0.8s;
z-index: 2px;
}