title: Override CSS class using JS
body: <p>I am using Reveal JS. This is the CSS that I want to override:</p>
  
  <pre><code>.reveal section img {...
  </code></pre>
  
  <p>Using one of the methods below (or something better), how can I use JS to override that?</p>
  
  <pre><code>document.getElementById(image1).classList.add("red"); // I tried creating a CSS class called "red" but it doesn't overide the original
  document.getElementById(image1).style.boxShadow = "red"; // this doesn't overide the original theme CSS
  </code></pre>