title: How to focus a paper-input in lit-element
body: <p>I have a <code>&lt;paper-input&gt;</code> element on my page that I want selected when the page loads. I tried to focus it when the page is first updated but that hasn't worked.</p>
  
  <pre><code>firstUpdated() {
      this.shadowRoot.querySelector('#input').focus();
  }
  </code></pre>
  
  <p><a href="https://www.webcomponents.org/element/@polymer/paper-input/elements/paper-input#description" rel="nofollow noreferrer">The paper-input page</a> suggests that setting <code>tabindex</code> is required for <code>input.focus()</code> to work, so I did that as well and it did not work. I have also tried the solutions suggested for <a href="https://stackoverflow.com/questions/24496590/polymer-focus-on-paper-input-or-core-input-element">this SO question</a> about <code>paper-input</code> in polymer, and none of them worked.</p>
  
  <p>Is there a way to focus a <code>paper-input</code> in lit-element?</p>