Bug: Validator does not recognize 8th argument of animation property

See [MDN article on animation property values ](https://developer.mozilla.org/en-US/docs/Web/CSS/animation)

```
/* 
It doesn't recognize the 8th argument, animation-play-state
https://developer.mozilla.org/en-US/docs/Web/CSS/animation
*/
.loading-mask {
    animation: fadein 2000ms linear 750ms infinite normal forwards running;
}
```