.box {
    width: 200px;
    height: 200px;
    line-height: 200px;
    color: white;
    text-align: center;
    vertical-align: middle;
    background: -webkit-linear-gradient(red, #ccc); /* For Safari 5.1 to 6.0 */
    background: -o-linear-gradient(red, #ccc); /* For Opera 11.1 to 12.0 */
    background: -moz-linear-gradient(red, #ccc); /* For Firefox 3.6 to 15 */
    background: linear-gradient(red, #ccc); /* Standard syntax */
}