Add CSS for .ng-invalid class (and possibly .ng-valid if it looks good)

[SynbioLucas]

Color feedback for invalid form input elements. Something like this would work, but whatever looks good is fine:

input.ng-invalid {
  border: 1px solid red;
}
input.ng-valid {
  border: 1px solid green;
}

(via here)

These classes will automatically be applied to input elements as users enter stuff.

[SynbioLucas]

@felixekn This should actually be a custom error class, not ng-invalid, since we're not using angular's validation framework anymore.