title: CSS difference between 0 and 0em
body: <p>Is there any difference between </p>
  
  <pre><code>margin: 0;
  </code></pre>
  
  <p>and </p>
  
  <pre><code>margin: 0em;
  </code></pre>
  
  <p>I didn't notice anything, but my teacher keeps telling me that it's not the same.</p>