function findMostSpecificMatchedCSSRule(matchedCSSRules = [], isDeclarationOfInterest) {
  let mostSpecificRule;
  for (let i = matchedCSSRules.length - 1; i >= 0; i--) {
    if (isDeclarationOfInterest(matchedCSSRules[i].rule.style)) {
      mostSpecificRule = matchedCSSRules[i].rule;
      break;
    }
  }

  if (mostSpecificRule) {
    return {
      type: 'Regular',
      ...mostSpecificRule.style,
      parentRule: {
        origin: mostSpecificRule.origin,
        selectors: mostSpecificRule.selectorList.selectors,
      },
    };
  }
}
Finds the most specific directly matched CSS font-size rule from the list.

@param {Array<LH.Crdp.CSS.RuleMatch>} matchedCSSRules
@param {function(LH.Crdp.CSS.CSSStyle):boolean|string|undefined} isDeclarationOfInterest
@return {NodeFontData['cssRule']|undefined}