title: tkinter keeping window on top all times on MacOS
body: <p>I'm trying to create a screen "curtain" which blocks parts of the screen except for the mouse cursor's vicinity.
  On windows, using <code>root.wm_attributes("-topmost", "true")</code> keeps the window on top, even if I focus on another app, perfectly. However, upon running the code on MacOS, if the focus for the window is lost, it will not keep itself on topmost.
  What would be the MacOS equivalent to <code>-topmost</code> window manager attribute which will always keep the window on top, regardless of focus? </p>
  
  <pre><code>import tkinter as tk
  
  class TransparentWindow(tk.Toplevel):
      """
      This class is just a Toplevel window.
      """
      def __init__(self, background="white", opacity=0.7):
          super(TransparentWindow, self).__init__()
          #self.master = master
          self.configure(background=background)
          self.overrideredirect(True)
          self.wm_attributes("-alpha", opacity)
          self.wm_attributes("-topmost", "true")
          self.lift()
  
  
  if __name__ == '__main__':
      root = tk.Tk()
      TransparentWindow() 
      root.mainloop()
  </code></pre>
  
  <p>Running this code in a High Sierra Virtual Machine resulted in the Toplevel not constantly being on top when another window is selected.</p>