code: private void installClientDecorations(JRootPane root) {
          installBorder(root);
          if (root.getParent() instanceof JFrame || root.getParent() instanceof JDialog) {
              if (PlatformUtils.isMac()) {
                  makeFrameBackgroundTransparent(root);
              } else {
                  shapeWindow(root);
              }
          }
  
          JComponent titlePane = createTitlePane(root);
  
          setTitlePane(root, titlePane);
          installWindowListeners(root, root.getParent());
          installLayout(root);
          if (window != null) {
              root.revalidate();
              root.repaint();
          }
      }
docs: Installs the necessary state onto the JRootPane to render client
  decorations. This is ONLY invoked if the <code>JRootPane</code> has a
  decoration style other than <code>JRootPane.NONE</code>.
  
  @param root the JRootPane.