Linear gradient in Chrome and Safari browsers

I am having trouble showing a linear gradient in Safari and Chrome. In Firefox it shows up fine.

I am trying:

background: -webkit-linear-gradient(center top , #9E9E9E, #454545) repeat scroll 0 0 transparent;   
background:    -moz-linear-gradient(center top , #9E9E9E, #454545) repeat scroll 0 0 transparent;
background:     -ms-linear-gradient(center top , #9E9E9E, #454545) repeat scroll 0 0 transparent;
background:      -o-linear-gradient(center top , #9E9E9E, #454545) repeat scroll 0 0 transparent;

Thanks you for your help.