How can I make box-shadow appear above a div?

Question

Here is an example of what I'm trying to accomplish.

The box-shadow from the upper div won't appear on top of the div below it. From what I understand, I need to set the z-index so it will appear on top and that only works on elements with position: relative; but it's still not appearing.

What am I doing wrong?

#top {
    width: 100%;
    height: 100px;
    box-shadow: 3px 3px 3px #333;
    background-color: blue;
}

#middle {
    width: 100%;
    height: 200px;
    z-index: 0;
    position: relative;
    background-color: orange;
}

#innerMiddle {
    width: 200px;
    height: 200px;
    margin: 0 auto;
    background-color: green;
}

<div id="top">
</div>

<div id="middle">
    <div id="innerMiddle">
    </div>
</div>

Answer 1

It's #top and its box-shadow that you want to appear on top, so give that position: relative instead of giving position: relative to #middle. There's no need for z-index: 0.

http://jsfiddle.net/thirtydot/QqME6/1/

#top {
    width: 100%;
    height: 100px;
    box-shadow: 3px 3px 3px #333;
    background-color: blue;
    
    position: relative;
}

#middle {
    width: 100%;
    height: 200px;
    background-color: orange;
}

#innerMiddle {
    width: 200px;
    height: 200px;
    margin: 0 auto;
    background-color: green;
}

<div id="top">
</div>

<div id="middle">
    <div id="innerMiddle">
    </div>
</div>

Answer 2

Change your CSS to:

#top {
    width: 100%;
    height: 100px;
    box-shadow: 3px 3px 3px #333;
    background-color: blue;
    position:relative;
    z-index:1;
}

#middle {
    width: 100%;
    height: 200px;
    z-index: 0;
    position: relative;
    background-color: orange;
}

<div id="top">
</div>

<div id="middle">
    <div id="innerMiddle">
    </div>
</div>