final ThemeConfiguration modernTheme = new ModernNatTableThemeConfiguration();
modernTheme.addThemeExtension(new ModernGroupByThemeExtension());
final ThemeConfiguration darkTheme = new DarkNatTableThemeConfiguration();
darkTheme.addThemeExtension(new DarkGroupByThemeExtension());
natTable.setTheme(modernTheme);
// add a border on every side of the table
natTable.addOverlayPainter(new NatTableBorderOverlayPainter());