Prevent GUI Window border from disappearing when window is active

I'm using a GUI window in my app with the following code:

 GUILayout.Window (0, windowRect, DoGui, "");

When the window becomes active, the border around the window disappears. Does anyone know how to prevent the window from disappearing. I've tried the following code:

     int border = 20;
     
     GUI.skin.window.border.left = border;
     GUI.skin.window.border.right = border;
     GUI.skin.window.border.top = border;
     GUI.skin.window.border.bottom = border;

But it doesn't work.