title: Find style references that don't exist
body: <p>Is there a tool that will find for me all the css classes that I am referencing in my HTML that don't actually exist?</p>
  
  <p>ie. if I have &lt;ul class="topnav" /&gt; in my HTML and the topnav class doesn't exist in any of the referenced CSS files.</p>
  
  <p>This is similar to <a href="https://stackoverflow.com/questions/33242/how-can-i-find-unused-images-and-css-styles-in-a-website">SO#33242</a>, which asks how to find unused CSS styles. This isn't a duplicate, as that question asks which CSS classes are not used.  This is the opposite problem.</p>