gecko-dev/layout/reftests/css-ui-valid/output/style.css

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

output.notvalid {
  color: green;
}
output.notvalid:-moz-ui-valid {
  color: red;
}

output.valid {
  color: red;
}
output.valid:-moz-ui-valid {
  color: green;
}

output.ref {
  color: green;
}