[jQuery] jQuery Corner problem

[jQuery] jQuery Corner problem

I'm trying to use the corner plugin (<a href="http://www.malsup.com/jquery/corner" target="_blank"> http://www.malsup.com/jquery/corner</a>) to create rounded corners on a div.
First I display a div that covers the whole page and has a black, transparent background.
Then I show another div, white background, centered on the screen.
So it's a kind of popup.
The problem is that when I just use <span style="font-family: courier new,monospace;">$(...).corner()</span>, nothing happens.
But if I color the corners with <span style="font-family: courier new,monospace;">$(...).corner("cc:#000")</span>, I can see the corner, but it's black.
Is there something wrong with the following code?
<span style="font-family: courier new,monospace;">$("#overlay_bg").width($(document).width());</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;">
$("#overlay_bg").height($(document).height());</span><br style="font-family: courier new,monospace;"><br style="font-family: courier new,monospace;"><span style="font-family: courier new,monospace;">$("#overlay_fg").width(400);</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;"></span><span style="font-family: courier new,monospace;">$("#overlay_fg").center();</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;">$("#overlay_fg").corner();</span>
<span style="font-family: courier new,monospace;">$("#overlay_bg").show();</span><br style="font-family: courier new,monospace;">
<span style="font-family: courier new,monospace;">$("#overlay_fg").slideDown("slow");</span>
Thanks for checking!