title: Android BottomSheetDialogFragment has color behind rounded corners
body: <p>I'm using <code>BottomSheetDialogFragment</code> and I'm rounding the corners of top right/left and it's working properly but I noticed that behind the rounded corners, it's not transparent and it's very annoying.</p>
  
  <p>It's noticeable in the below screenshot:</p>
  
  <p><a href="https://i.stack.imgur.com/tmLrg.png" rel="noreferrer"><img src="https://i.stack.imgur.com/tmLrg.png" alt="enter image description here"></a></p>
  
  <p>How do I make them transparent?</p>