title: How to let the users style a web component with their own CSS?
body: <p>I know we can use CSS to style elements of a web component. But how can I allow the user style my web component?</p>
  
  <p>For example let's say I'm making a video player but I want the people who use my component be able to set the play button or the progress bar to the color of their brands. The <strong><a href="http://css-tricks.com/modular-future-web-components/" rel="nofollow">shadow boundary</a></strong> seems to prevent it for good. But what if I want it?</p>
  
  <p>It would be great if the users don't have to use attributes for such styling tasks. Standard CSS would be great but I'm not sure if it's possible as of late January 2015?</p>