@Override
	public void ensureCloseButtonCreated() {
		super.ensureCloseButtonCreated();

		if( _closeButtons == null )
			return;

		// make sure that close buttons use our icon and do not fill background
		for( JButton closeButton : _closeButtons ) {
			if( closeButton.getIcon() != closeIcon )
				closeButton.setIcon( closeIcon );
			if( closeButton.isContentAreaFilled() )
				closeButton.setContentAreaFilled( false );
		}
	}
Actually does nearly the same as super.paintContentBorder() but
  - not invoking paintContentBorder*Edge() methods
  - repaint selection
flatlaf-jide-oss/src/main/java/com/formdev/flatlaf/jideoss/ui/FlatJideTabbedPaneUI.java