I have craeted a greyed out layer that sites above the website when called, and inside that I have another div, and its this div that is confusing me.

I am using z-index to try and get the inner div to not adopt the alpha transpareny of its parent div, and its just not working.

Here is the css:

Code:
#cover{
	position:absolute;
	top:0px;
	left:0px;
	overflow:hidden;
	width:100%;
	height:1500px;
	background-color:#000000;
	opacity:0.5;
	MozOpacity:0.5;
	z-index:10;
	filter:alpha(opacity=50);
	text-align:center
}
#warning{
	margin:auto;
	position:relative;
	width:400px;
	height:200px;
	background-color:white;
	color:black;
	padding:10px;
	opacity:1.0;
	MozOpacity:1.0;
	z-index:100;
	filter:alpha(opacity=100);
	top:200px;
	margin-left:auto;
	margin-right:auto;
}
Here is the html:

HTML Code:
<div id="cover">
<div id="warning">
<p align="center">
<input type="button" onClick="javascript:location.href=('http://www.);" value="Return to admin" />
</p>
</div>
</div>	
Its working fine and appearing when i want it too, but the warning div adopts the transparency of cover and the effect isnt right, as i wont warning to be a solid colour.

Cheers