title: How to select :host with a class in css for web components?
body: <p>In the new v1 web components specs, you can use <code>:host</code> to target the custom element. But then I attached a class <code>A</code> to the custom element, and had a css selector <code>:host.A</code>, but its styles are not being applied. Does anyone know how to fix this?</p>
  
  <p>Thanks</p>