title: react-testing-library include third party css in snapshot
body: <p>I am loading third party css manually by injecting into <code>index.html</code>.
  I created snapshot test for react component. It outputs only the dom that has been generated.</p>
  
  <p>Is there any way to include the css classed used in component to be included in generated snapshot to determine if anything has been changed?</p>
  
  <p>Or is there any other way to find out changes how many components are affected by changes in third party css changes?</p>