css3 drop shadow under another div, z-index not working

i'm trying to use a drop shadow to make it look like one div (the header) is "above" another. my problem is that the "middle" div is covering the drop shadow. i tried using z-index to put the header div about the middle div, but it's not working (the shadow is still being covered). when i put a break between the divs, i can see the shadow and therefore i know that part of the code is working properly. i have the following html code:

<div id='portal_header_light'>
<img src="Home.png" height="32px" \>
<img src="Wrench.png" height="32px" \>
</div>
<div id='middle'></div>

and this css:

#portal_header_light {
	font-family:Arial, Helvetica, sans-serif;
	font-size:12px; text-align:center;
	-moz-border-radius: 3px 3px 3px 3px;
	-webkit-border-radius: 3px 3px 3px 3px;
	padding: 0px 3px 0px 3px;
	background: -moz-linear-gradient(center top, #999999 0%,#ffffff 100%);
	background: -webkit-gradient(linear, left top, left bottom, color-stop(0, #999999),color-stop(1, #ffffff));
	
	-webkit-box-shadow: 0px 1px 10px rgba(0, 0, 0, 0.3);
	-moz-box-shadow: 0px 1px 10px rgba(0, 0, 0, 0.3);
	box-shadow: 0 1px 10px rgba(0, 0, 0, 0.3);

	z-index:5;
}

#middle{
	height:308px;
	background-color:white;
	z-index:-1;
}

any ideas? thanks.

The z-index property works only on positioned elements. Those include position: relative, position: absolute, position: fixed, and position: sticky elements.

Try to give your div #middle a position: relative.

Try an inset box shadow ON the element you want to appear under.

.element-that-is-to-be-under{
    -webkit-box-shadow: inset 0 8px 4px -4px #ddd;
    -moz-box-shadow: inset 0 8px 4px -4px #ddd;
    box-shadow: inset 0 8px 4px -4px #ddd;
}

Doing this will alleviate the z-index shuffle and you'll be much happier in the long run.

Building on the other answers here, I found this worked better by putting position: relative on #portal_header_light, instead of #middle. Then I didn't have to have z-index: -1, which (at least in Chrome) messed up the cursor link hover effects and caused some other odd issues.

http://jsfiddle.net/thaddeusmt/m6bvZ/

Here is the simplified code:

<div id="portal_header_light">Header Content</div>
<div id="middle">Test Content</div>

#portal_header_light {
  position: relative;
  padding: 3px;
  background: #eee;
  -webkit-box-shadow: 0px 4px 10px -2px rgba(0, 0, 0, 0.3);
  -moz-box-shadow: 0px 4px 10px -2px rgba(0, 0, 0, 0.3);
  box-shadow:  0 4px 10px -2px rgba(0, 0, 0, 0.3);
  z-index:5;
}

#middle{
  height:308px;
  background-color:#fee;
  padding: 3px;
}