In Style Manager -> All Style Options there is a box near the bottom "Additional CSS" or something like that... add this code:
Code:
.page {
-moz-box-shadow: 3px 3px 4px #000;
-webkit-box-shadow: 3px 3px 4px #000;
box-shadow: 3px 3px 4px #000;
}
page is the element name you want to put the shadow around... the original link explains the numbers, play with the numbers to get the effect you want.