title: How do I tint an application window like this one?
body: <p>I am very new to OSX development.</p>
  
  <p>How do I tint an application to dark gray like this one did?</p>
  
  <p><img src="https://i.stack.imgur.com/4fiIK.png" alt="enter image description here"></p>
  
  <p>is it possible to do that from interface builder? If not, how do I do that from code?</p>