code: public void paintTabbedPaneTabAreaBackground(SynthContext context, Graphics g, int x, int y, int w, int h, int orientation) {
          if (orientation == JTabbedPane.LEFT) {
              AffineTransform transform = new AffineTransform();
  
              transform.scale(-1, 1);
              transform.rotate(Math.toRadians(90));
              paintBackground(context, g, y, x, h, w, transform);
          } else if (orientation == JTabbedPane.RIGHT) {
              AffineTransform transform = new AffineTransform();
  
              transform.rotate(Math.toRadians(90));
              transform.translate(0, -(x + w));
              paintBackground(context, g, y, 0, h, w, transform);
          } else if (orientation == JTabbedPane.BOTTOM) {
              AffineTransform transform = new AffineTransform();
  
              transform.translate(x, y);
              paintBackground(context, g, 0, 0, w, h, transform);
          } else {
              paintBackground(context, g, x, y, w, h, null);
          }
      }
docs: Paints the background of the area behind the tabs of a tabbed pane. This
  implementation invokes the method of the same name without the
  orientation.
  
  @param context     SynthContext identifying the <code>JComponent</code>
  and <code>Region</code> to paint to
  @param g           <code>Graphics</code> to paint to
  @param x           X coordinate of the area to paint to
  @param y           Y coordinate of the area to paint to
  @param w           Width of the area to paint to
  @param h           Height of the area to paint to
  @param orientation One of <code>JTabbedPane.TOP</code>, <code>
  JTabbedPane.LEFT</code>, <code>
  JTabbedPane.BOTTOM</code> , or <code>
  JTabbedPane.RIGHT</code>