title: material-ui overlay div behind Drawer Component
body: <p>I'm using material-ui in a React app. I'm using the side menu "Drawer" component but cannot figure out how to include the semi-transparent background overlay behind the open menu.</p>
  
  <p><a href="http://www.material-ui.com/#/components/drawer" rel="nofollow noreferrer">http://www.material-ui.com/#/components/drawer</a></p>