[webcomponents] Combining :host-context and :host (#359)

Is there a way to combine the `:host-context` and `:host` selectors according to the spec? If it's not currently supported, what would the correct syntax look like?

```css
:host-context(.foo) :host(.bar) { }
:host-context(.foo :host(.bar)) { }
:host-context(.foo).bar { }
/* .. etc .. */
```

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Reply to this email directly or view it on GitHub:
https://github.com/w3c/webcomponents/issues/359