title: Adding drop-shadow to map layer
body: <p>I'm a UI Designer, and my client will use mapbox for his website. I'm working on a custom style where I want to make the whole map white with a drop-shadow.</p>
  <p>I know only basics for now, so there's my question. <strong>How can I add a drop-shadow for 'land' layer?</strong> I just want to know if it's possible and it would be awesome to know the solution.</p>
  <p>Thanks,
  Robert</p>