Enable shadows for an image element on a 2D screen

I have an element group colored in white. I want to have a shadow behind it so that it gives a 3D feel.

Here is what I want it to look like:

Here is what I have manged so far:

One thing I thought of was creating this using HTML and CSS but that would mean changing everything I have done so far.

Is there any other way of doing the same thing.

Have a 9 slice (are those in the main build yet?) of a drop shadow that you can resize to fit your UI box?