Simulate two backgrounds 2V

Question

Ok... i manage two create it.
to those who aren't familiar with it i've wanted to create i background image with a gradiente and then a "frontground" image a plain white thing that all my page will go there.
i manage to do it ...but i noticed there was a 3rd element http://www.libertyseguros.pt/ between the gradient page and the white page there's a shadow so it can highlight more the white page...onde again i don't know how to place it here is my code

content {

  width: 970px;
 margin: auto;
 margin-top:0px;
 background: white;
 height: 1000px;
 border:1px solid silver;
 z-index:100