Find unused CSS rules on a page

find-unused-css.js

(function() {
  for (var ssi = 0; ssi < document.styleSheets.length; ssi++) {
    let rules;
        try {
        rules = document.styleSheets[ssi].cssRules || [];
    } catch (e) {
        rules = []
    }
      
    var sheetHref = document.styleSheets[ssi].href || 'inline';
 
    for (var ri = 0; ri < rules.length; ri++) {
      if (!document.querySelectorAll(rules[ri].selectorText).length) {
        console.log(`${sheetHref}: "${rules[ri].selectorText}" not found.`);
      }
    }
  }
})();