input[type=submit]:hover 
    background-image: -webkit-gradient(linear, left top, left bottom, from(#b6e2ff), to(#6ec2e8));
    background-image: -moz-linear-gradient(top left 90deg, #b6e2ff 0%, #6ec2e8 100%);
    background-image: linear-gradient(top left 90deg, #b6e2ff 0%, #6ec2e8 100%);

input[type=submit]:active 
    background-image: -webkit-gradient(linear, left top, left bottom, from(#6ec2e8), to(#b6e2ff));
    background-image: -moz-linear-gradient(top left 90deg, #6ec2e8 0%, #b6e2ff 100%);
    background-image: linear-gradient(top left 90deg, #6ec2e8 0%, #b6e2ff 100%);

This should result in the following: