.grayscale {
  -webkit-filter: grayscale(100%); /* Ch 23+, Saf 6.0+, BB 10.0+ */
  filter: grayscale(100%) ; /* FF 35+ */
}

.grayscale:hover {
    
  -webkit-filter: grayscale(0%); /* Ch 23+, Saf 6.0+, BB 10.0+ */
  filter: grayscale(0%); /* FF 35+ */
  -webkit-transition: all .9s ease-in-out;  
}