count-styles.js

var elems = document.getElementsByTagName('*');
var usages = {};

for (var i = 0; i < elems.length; i++) {
  var elemStyles = document.defaultView.getComputedStyle(elems[i], null);
  var font = elemStyles.getPropertyValue('font-family').split(',')[0];
  var weight = elemStyles.getPropertyValue('font-weight');
  var style = elemStyles.getPropertyValue('font-style');

  var fontName = `${font} ${weight} ${style}`;

   if ((fontName.indexOf('Sephora') !== -1) || (fontName.indexOf('avalon') !== -1)) {
      usages[fontName] = (usages[fontName] || 0) + 1;
   }
}

console.table(usages)