code: protected void paintContentBorder(SeaGlassContext ss, Graphics g, int tabPlacement, int selectedIndex) {
          int    width  = tabPane.getWidth();
          int    height = tabPane.getHeight();
          Insets insets = tabPane.getInsets();
  
          int x = insets.left;
          int y = insets.top;
          int w = width - insets.right - insets.left;
          int h = height - insets.top - insets.bottom;
  
          switch (tabPlacement) {
  
          case LEFT:
              x += calculateTabAreaWidth(tabPlacement, runCount, maxTabWidth);
              w -= (x - insets.left);
              break;
  
          case RIGHT:
              w -= calculateTabAreaWidth(tabPlacement, runCount, maxTabWidth);
              break;
  
          case BOTTOM:
              h -= calculateTabAreaHeight(tabPlacement, runCount, maxTabHeight);
              break;
  
          case TOP:
          default:
              y += calculateTabAreaHeight(tabPlacement, runCount, maxTabHeight);
              h -= (y - insets.top);
          }
  
          SeaGlassLookAndFeel.updateSubregion(ss, g, new Rectangle(x, y, w, h));
          ss.getPainter().paintTabbedPaneContentBackground(ss, g, x, y, w, h);
          ss.getPainter().paintTabbedPaneContentBorder(ss, g, x, y, w, h);
      }
docs: Paint the content pane's border.
  
  @param ss            the SynthContext.
  @param g             the Graphics context.
  @param tabPlacement  the side the tabs are on.
  @param selectedIndex the current selected tab index.