title: Opacity for images in body when open a sidenav
body: <p>I want to change the opacity of my body when my sidenav opens. 
  It works perfectly! But now I am faceing the problem, that my images won't get this effect, they stay as bright as before.
  How can I change it, that the images and all the other stuff, like iframe content, gets the same effect?</p>
  
  <p>This is the working code for the body opacity:</p>
  
  <pre><code>function openNav() {
      document.getElementById("mySidenav").style.width = "250px";  
      document.body.style.backgroundColor = "rgba(0,0,0,0.6)";
  }
  </code></pre>
  
  <p>Regards</p>