chromium/third_party/blink/web_tests/css3/selectors3/xml/css3-modsel-155b.css

  p { background: lime; }
  .two\ words { background: red; }

  /* the "." and "~=" forms match on a space separated list of words.
  In such a list, a word containing a space can never match, since it
  would by definition be two words. */