code: function getStylesheets(window, options) {
      if (Array.isArray(options.media) === false) {
          options.media = [options.media];
      }
  
      const media = _.union(['', 'all', 'screen'], options.media);
      const elements = window.document.querySelectorAll('link[rel="stylesheet"]');
  
      return Array.prototype.map.call(elements, (link) => ({
          href: link.getAttribute('href'),
          media: link.getAttribute('media') || ''
      }))
      .filter((sheet) => media.indexOf(sheet.media) !== -1)
      .map((sheet) => sheet.href);
  }
docs: Extract stylesheets' hrefs from dom
  @param  {Object}  window     A jsdom window
  @param  {Object}  options    Options, as passed to UnCSS
  @return {Array}