Styles & Templates --> Search in Templates --> Search for Text --> additonal.css (In style of your choice) --> Add to additional css...
Try Something like this in the
additional.css
Code:
.body_wrapper {
-moz-box-shadow: 4px 4px 5px #FF0000;
-webkit-box-shadow: 4px 4px 5px #FF0000;
box-shadow: 4px 4px 5px #FF0000;
}
Code:
Change #FF0000 to your shadow colour / color