title: How to change background overlay of ContentDialog uwp
body: <p>I am developing UWP Win10 App using VS2015. I am using ContenDialog to show a Modal Window / Popup. I need to change the Background Overlay color of ContentDialog. How to do this. There is no option/property even in the inner Style too.</p>
  
  <p>I need to change the Overlay White Dim color to some other color like Blackish overlay/dim color etc...</p>
  
  <p>See the pic.</p>
  
  <p><a href="https://i.stack.imgur.com/QndTd.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/QndTd.png" alt="enter image description here"></a></p>