select2/docs/_sass/_alert.scss

.alert {
  padding: 20px;
  margin: 20px 0;
  border: 1px solid #eee;
  border-left-width: 5px;
  border-radius: 3px;
  background: #fff;
  color: #333;

  h4 {
    margin-top: 0;
    margin-bottom: 5px;
    font-size: 18px;
  }

  &-danger {
    border-left-color: #CE4844;

    h4 {
      color: #CE4844;
    }
  }

  &-info {
    border-left-color: #1B809E;

    h4 {
      color: #1B809E;
    }
  }

  &-warning {
    border-left-color: #AA6708;

    h4 {
      color: #AA6708;
    }
  }
}