Cant get submit hover button to show on top of regular submit button

I am trying to get my submit button to change when it is hovered over. The only problem is that I cannot get the hover effect to overlap the regular submit button. Here is the code I am trying.

body #gform_wrapper_3 .gform_footer input[type=image] {
	padding: 0;
	display: block;
	margin-left: -79px !important;
	margin-top: -11px !important;
	background: url(http://www.certifiedtopmovers.com/wp-content/uploads/SubmitButton.png) center top no-repeat !important;
	height: 76px !important;
	width: 242px !important;
	border: none !important;
	z-index: 98 !important;
}

body #gform_wrapper_3 .gform_footer:hover input[type=image] {
	padding: 0;
	display: block;
	margin-left: -79px !important;
	margin-top: -11px !important;
	background: url(http://www.certifiedtopmovers.com/wp-content/uploads/SubmitButtonHover.png) center top no-repeat !important;
	height: 76px !important;
	width: 242px !important;
	border: none !important;
	z-index: 99 !important;
}

and you can view the form here. http://www.certifiedtopmovers.com

Thanks. This has been a problem for me on many sites so hopefully someone can shed some light on the solution.