gecko/layout/reftests/css-ui-valid/textarea/style.css

/* Override default style */
textarea:invalid {
  box-shadow: none;
}

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

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