angular-cn/public/docs/_examples/cb-form-validation/ts/forms.css

.ng-valid[required] {
  border-left: 5px solid #42A948; /* green */
}

.ng-invalid {
  border-left: 5px solid #a94442; /* red */
}

.ng-valid.required {
  border-left: 5px solid #42A948; /* green */
}