AFAIK, here’s the only currently supported background-image values (both vendor extensions):

background-image: -webkit-gradient(
	linear,
	left top,
	left bottom,
	color-stop(0, #FFFFFF),
	color-stop(1, #000000)
);
background-image: -moz-linear-gradient(
	center top,
	#FFFFFF 0%,
	#000000 100%
);
background-image: linear-gradient(
	top,
	#FFFFFF 0%,
	#000000 100%
);
filter: progid:DXImageTransform.Microsoft.Gradient(
	StartColorStr='#FFFFFF',
	EndColorStr='#000000',
	GradientType=0
);