title: How to create a new html element?
body: <p>I tried to create a new HTML element, called test: <code>&lt;test&gt;some text&lt;/test&gt;</code></p>
  
  <p>I tried to prototyping it like this: <code>HTMLUnknownElement.prototype.style.backgroundColor = "red";</code> but it doesn't work.</p>
  
  <p>Could you please help me, how to manage it?</p>
  
  <p>Thanks in advance,</p>