title: CSS center an element
body: <p>Why do 'margin left and right set to auto and max. and min. width' center an element?</p>
  
  <pre><code>#header{
      max-width: 1400px;
      min-width: 360px;
      margin-left: auto;
      margin-right: auto;
  }
  </code></pre>
  
  <p>I do not get it. </p>