styles.scss

@import "node_modules/bootstrap/scss/bootstrap";
@import "node_modules/bootstrap/scss/variables";

.app {
  app-nav {
    display: block;
    margin-bottom: 20px;
  }

  input.ng-invalid.ng-touched {
    border-color: red;
  }

  form.ng-submitted {
    input.ng-invalid {
      border-color: red;
    }
  }

  span.error-msg {
    color: red;
  }
}