CSS: Support of chaining pseudo class

CSS 3 Spec: https://www.w3.org/TR/selectors-3/#selector-syntax

```
.controls-arrow:hover:before
```

Work around is:

```

.controls-arrow:hover:before {

}

```

I think the spec says that any simple pseudo class can be chained but only one pseudo element can occur at the end. Not sure yet how to support that in the Tag syntax.