public static function css_to_string($css){
    if ( \is_string($css) ){
      return ' style="'.bbn\str::escape_dquotes($css).'"';
    }
    else if ( \is_array($css) && \count($css) > 0 ){
      $st = '';
      foreach ( $css as $prop => $val ){
        $st .= $prop.':'.$val.';';
      }
      return ' style="'.bbn\str::escape_dquotes($st).'"';
    }
  }