title: change the color of the close button in fullscreen
body: <p>how to change button close (x) in flutter fullscreen dialog ?? Is that the default button for widgets that cannot be changed?
  I want to change the default color (white) to black, because later the color of the appbar is white.</p>
  
  <p><a href="https://i.stack.imgur.com/lmMDr.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lmMDr.jpg" alt=""></a></p>