palemoon-dev/platform/layout/reftests/css-ui-valid/button/style.css

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

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

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