Customising the WordPress Toggle menu [toggle]

Hi,

Can somebody please tell me how I can change the toggle menu image on hover? This is doing my head in! I want to change the background image (+ icon) to white like it’s active state after the user has clicked on a menu item.

Please take a look and scroll to the bottom of the page. My toggle menu is contained within a [tab] menu.

The CSS:

.toggle {
    padding: 0 0 2px 0;
}
.toggle .trigger {
	background-color: #f5f5f5;
	background: -moz-linear-gradient(bottom, #F2F2F2 0px, #ffffff 100%);
	background: -webkit-gradient(linear,left bottom,left top, color-stop(0, #f2f2f2),color-stop(1, #ffffff));
	border: 1px solid #dddddd;
	border-radius: 5px;
	-moz-border-radius: 5px;
	-webkit-border-radius: 5px;
	color: #666666;
	display: block;
	padding: 10px 12px 10px 40px;
	position: relative;
	text-decoration:none;
	height:1%;
	}

.toggle .trigger span {
	background: url(includes/images/toggle.png) 0 0 no-repeat;
	display: block;
	position: absolute;
	top: 9px;
	left: 10px;
	text-indent: -9999px;
	width: 22px;
	height: 20px;
	}

.toggle .trigger:hover,
.toggle .active {
	background:#333399;
	color:#fff;
	}
.toggle .active span {
	background: url(includes/images/toggle-white.png) 0 0 no-repeat;
	background-position: 0 -20px;
	}

.toggle .box {
	background-color: #fafafa;
	border: 1px solid #dddddd;
	border-radius: 5px;
	-moz-border-radius: 5px;
	-webkit-border-radius: 5px;
	padding: 20px;
	}

Please help! Thank you.