function findMostSpecificCSSRule(matchedCSSRules, property) {
  /** @param {LH.Crdp.CSS.CSSStyle} declaration */
  const isDeclarationofInterest = (declaration) => findSizeDeclaration(declaration, property);
  const rule = FontSize.findMostSpecificMatchedCSSRule(matchedCSSRules, isDeclarationofInterest);
  if (!rule) return;

  return findSizeDeclaration(rule, property);
}
Finds the most specific directly matched CSS font-size rule from the list.

@param {Array<LH.Crdp.CSS.RuleMatch>|undefined} matchedCSSRules
@param {string} property
@return {string | undefined}