gtk2/testsuite/css/change/test4.css

/* test negations */

box {
  color: red;
}

label.a:not(:hover) {
  color: green;
}

label.b:not(:hover):backdrop {
  color: green;
}

box:not(:hover) label.c {
  color: green;
}

box:not(:hover):backdrop label.d {
  color: green;
}

box:not(:hover):backdrop label.e:not(.f) {
  color: green;
}