angular-cn/aio/content/examples/forms/ts/src/forms.css

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

.ng-invalid:not(form)  {
  border-left: 5px solid #a94442; /* red */
}
/* #enddocregion */