Logs all the unused style rules in loaded stylesheets.

log-unused-style-rules.js

function logUnusedStyleRules() {
  const unusedRules = [];

  [...document.styleSheets].forEach((sheet) => {
    [...sheet.rules].forEach((rule) => {
      if (!document.querySelector(rule.selectorText)) {
        unusedRules.push(rule);
      }
    });
  });

  console.log(unusedRules);
}

logUnusedStyleRules();