[jQuery] Interface Plugin draggables

[jQuery] Interface Plugin draggables


Hi,
I'm having a problem with the draggables:
I'm trying to get a half transparent background for the element I'm
dragging:
$('span[@id^=item' + strKey + ']').Draggable
(
{
revert : true,
autoSize : true,
ghosting : true,
onStart : function(helper)
{
$(helper).addClass('dragging');
}
}
);
And here the css:
.dragging {
backgound-color: #dddddd;
filter: alpha(opacity=50);
-moz-opacity: 0.5;
}
The class is assigned to the element, I can test this for eg with adding
a border. But the element always has a transparent background...
Michael