palemoon-dev/platform/layout/reftests/css-invalid/output/style.css

/* Override default style */
output {
  color: black;
}

output.notinvalid {
  color: green;
}
output.notinvalid:invalid {
  color: red;
}

output.invalid {
  color: red;
}
output.invalid:invalid {
  color: green;
}

output.ref {
  color: green;
}