tooltip bg color is transparent

I have added tooltip function in v8 and also modified bg color in CSS. I am getting tooltip. However, the background color is transparent. Any ideas?

.tool_tip_text
{
	font-size: 12px;
	width: 200px;
	height: 60px;
	border: 1px solid #7F7F7F;
	background-color: #33DDCC;
	padding: 4px;
	position: absolute;
	z-index: 1000;
	display: none;
}