Header Drop Shadow when scrolling

I came across an awesome drop shadow that I’d love to implement on Enfold, but I am horrendous with CSS programming. The idea came from http://www.jointheportauthority.com/ (scroll down, and you’ll see the header creates a drop shadow at the bottom.

Is there a way I can implement this in Enfold?

Currently I have my header set to shrink as the page is scrolled down, Id like to keep the shrinked header but add the shadow on the bottom..

Thanks!