title: Set borders for an expanded group item using ExpandableListView
body: <p>I'm trying to find a way of creating a material-styled <code>ExpandableListView</code>, and I'm using the example located at the <a href="http://www.google.com/design/spec/components/lists-controls.html#lists-controls-types-of-list-controls" rel="noreferrer">material design website</a>. The example I'm following is:</p>
  
  <p><img src="https://i.stack.imgur.com/FHiuJ.png" alt="Material Design Expandable List View"></p>
  
  <p>I'm trying to replicate the borders that appear at the top and bottom of the group when the group is expanded, but I don't know where to start. </p>
  
  <p>Can you help?</p>