code: protected void overrideTableExtractors() {
          StandardTableTarget.MAIN.setTableExtractor(new TableExtractor() {
              @Override
              public Table extract(final Table table) {
                  if (table instanceof Dialog) {
                      return ((Dialog) table).getContentTable();
                  } else if (table instanceof VisDialog) {
                      return ((VisDialog) table).getContentTable();
                  }
                  return table;
              }
          });
          StandardTableTarget.BUTTON.setTableExtractor(new TableExtractor() {
              @Override
              public Table extract(final Table table) {
                  if (table instanceof Dialog) {
                      return ((Dialog) table).getButtonTable();
                  } else if (table instanceof VisDialog) {
                      return ((VisDialog) table).getButtonsTable();
                  }
                  return table;
              }
          });
      }
docs: Since some multi-table Vis widgets do not extend standard Scene2D widgets, table extractors from multi-table
  actors need to be changed.