title: Apply CSS class to the body when opening a menu
body: <p>I'm currently working on a web project using LitElement, and I have a menu that shows when I click the hamburguer button, and closes when I click the close button or navigate to other page.</p>
  <p>My problem is that I want to apply the CSS property <code>overflow: hidden;</code> in order to stop the scroll for the rest of the page (because my menu has 100% width and height), and remove that property when the menu is closed.</p>
  <p>When I click the menu button, the component <code>Menu</code> is created, and when I click the close button (or navigate to another page) the component is deleted, so I have to apply the <code>overflow</code> in one component and remove it on another.</p>
  <p>So, my question is, how to do that?</p>