You would need to add a box shadow to the .head-wrap (the div that your header is inside of) like this –
box-shadow: 0 10px 25px #ccc;
-moz-box-shadow: 0 10px 25px #ccc;
-webkit-box-shadow: 0 10px 25px #ccc;
The 3 shadows above cover multi browser support (chrome, firefox, safari, etc).
Although you may not want this to appear on your homepage if you’re using a slider, since the shadow will appear on top of the slider background, and it won’t look right. To remove it from appearing on the homepage (only) if you’re using a slider, then add this right under the above code –