static int withBottomMargin_defaultWidth = 6;

static JPanel withBottomMargin(int w default withBottomMargin_defaultWidth, Component etc c) {
  ret swing(func -> JPanel {
    JPanel p = new JPanel(new BorderLayout);
    p.setBorder(BorderFactory.createEmptyBorder(0, 0, w, 0));
    p.add(c);
    ret p;
  });
}

Began life as a copy of #1004714