private static BufferedImage makeMinus(Color background) {
        BufferedImage image = makeIcon(background);
        Graphics2D g = (Graphics2D) image.getGraphics();
        g.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
        g.fillRect(4, 7, 8, 2);
        image.flush();
        return image;
    }