Why with the following code, I still can't get rid of drop shadows at the top and bottom. Although the drop shadows are "small", yet still they are there.

div#inner_container
{
width: 960px;
margin: 0px auto;
background-color: rgb(255, 255, 255);
box-shadow: 0 9px 0px 0px transparent,
            0 -9px 0px 0px transparent,
            12px 0 15px -4px rgba(255, 255, 255, 0.5),
            -12px 0 15px -4px rgba(255, 255, 255, 0.5);
position: relative;
z-index: 5000;
}