title: Round corner for BottomSheetDialogFragment Not working on API <21
body: <p>I am using <a href="https://stackoverflow.com/a/50929873/3248593">this solution</a> to round corners of dialog in <code>BottomSheetDialogFragment</code> and it works fine with API 21 and higher</p>
  
  <p><a href="https://i.stack.imgur.com/16Hm2.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/16Hm2.png" alt="enter image description here"></a></p>
  
  <p>But in Api &lt; 21 it removes the background and the rounded background goes away.
  <a href="https://i.stack.imgur.com/Ff0F2.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/Ff0F2.png" alt="enter image description here"></a>
  How to make the background rounded in API &lt; 21?
  If it is not possible to change the background, please help me change the background color instead.</p>