title: How to querySelect Lit-Element that is within another Lit-Element
body: <p>Parent element(x-app tag) displaying child1(x-counter),child2(child2-app) elements and whenever there is any change in child1, I would like to update it to child2 as well. So, in the parent I am trying to get the property of child 2 using querySelect but I am getting null value.</p>
  
  <p>ready(){
      super.ready();</p>
  
  <pre><code>document.querySelector('x-counter').addEventListener('valueChange',function(e){
    this.b = e.detail;
  
    const val = document.querySelector('x-app');
    console.log(val.querySelector('child2-app');
    val.a = this.b;
  
  
  });
  </code></pre>
  
  <p>}</p>
  
  <p>static get template(){</p>
  
  <pre><code>return html`
    &lt;x-counter&gt;&lt;/x-counter&gt;
  &lt;child2-app&gt;&lt;/child2-app&gt;
  
  `;
  </code></pre>
  
  <p>}</p>