@Override
			public void paint( Graphics g ) {
				// always fill background to paint over border on HiDPI screens
				g.setColor( popup.getBackground() );
				g.fillRect( 0, 0, getWidth(), getHeight() );

				super.paint( g );
			}
Scroll when user presses Up or Down keys.
flatlaf-core/src/main/java/com/formdev/flatlaf/ui/FlatPopupMenuUI.java