Overlay Opacity not working on my example

Overlay Opacity not working on my example


Hi there,
I'm using the standard UI library, latest version.
Im setting up the dialogs like this:
$(".popup").dialog({ autoOpen: false, resizable: false, width:
350, modal:true, overlay: { backgroundColor: "#000", opacity: 0.8} });
An example dialog is quite simple (adding it at the end of the page):
<div id="sendToFriends" title="Send to Friends" class="popup">

Put my stuff here


</div>
Not sure why, but the opacity never changes, whatever number I put on
it.
It happens on any browser FF, IE , Safari.
Any ideas?
Thanks,
Leonardo