drupal/modules/system/system-messages.css

/* $Id */

div.messages {
  background-color: #dfd;
  color: #000;
  margin-bottom: 0.25em;
  padding: 0.25em 0.5em;
}

.error {
  color: #e55;
}

div.error,
tr.error {
  background-color: #fcc;
}

.warning {
  color: #e09010;
}

div.warning,
tr.warning {
  background-color: #fcfca7;
}

.ok {
  color: #008000;
}

div.ok,
tr.ok {
  background-color: #dfd;
  color: #020;
}