title: How can I use ::theme pseudo-element?
body: <p>I've found an article about this pseudo-element <a href="http://tabatkins.github.io/specs/css-shadow-parts/#part-theme" rel="nofollow noreferrer">here</a>. So, I tried use it in my project, but it doesn't work.</p>
  
  <p>Maybe it has an experimental version? If so, how can I use it?</p>
  
  <p>Thanks</p>