Lists all CSS classes referred to in a document. Run this in a web browser console.

list-css-classes-in-document.js

(() => { // list all css classes referred to in the document
  const classes = new Set();
  function findClasses(el) {
    if(el.hasAttribute('class')) {
      const cls = el.getAttribute('class').split(' ');
      for(let cl of cls) {
        classes.add(cl);
      }
    }
    for(let child of el.children) {
      findClasses(child);
    }
  }
  findClasses(document.querySelector('body'));

  const sorted = Array.from(classes.values());
  sorted.sort();
  console.log(sorted.join("\n"));  
})();