title: Gray main window when open modal dialog in WPF
body: <p>When a modal dialog is opened from the main window, I want overlay the main window with gray color. Is there a standard solution in WPF to simulate this effect? </p>
  
  <p>Here one example: </p>
  
  <p><a href="https://i.stack.imgur.com/akXxW.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/akXxW.jpg" alt=""></a></p>