public function add_hamburger_button( $nav_output ) {

    $nav_name     = "nav-{$this->hamburger_config['theme_location']}";
    $state_output = sprintf(
      '<amp-state id="%s"><script type="application/json">%s</script></amp-state>',
      esc_attr( $this->hamburger_config['state_id'] ),
      wp_json_encode( $this->hamburger_config['state'] )
    );

    $hamburger_output = genesis_markup(
      [
        'open'    => '<button %s>',
        'close'   => '</button>',
        'context' => "{$nav_name}-toggle",
        'content' => $this->hamburger_config['label'],
        'echo'    => false,
      ]
    );

    return $state_output . $hamburger_output . $nav_output;

  }