code: public function index(HTTPRequest $r)
      {
          Requirements::css(BETTER_BUTTONS_DIR.'/css/betterbuttons_nested_form.css');
  
          return $this->customise(array(
              'Form' => $this->Form()
          ))->renderWith(BetterButtonNestedForm::class);
      }
docs: Render the form to the template
  @param  HTTPRequest $r
  @return SSViewer