gecko-dev/layout/reftests/css-invalid/textarea/style.css

/* Override default style */
textarea {
  border: 0px;
}

textarea.ref {
  background-color: green;
}

textarea:invalid {
  box-shadow: none;
}

textarea.notinvalid {
  background-color: green;
}
textarea.notinvalid:invalid {
  background-color: red;
}

textarea.invalid {
  background-color: red;
}
textarea.invalid:invalid {
  background-color: green;
}