title: modify pseudo select :after in javascript
body: <p>I have defined a css like</p>
  
  <pre><code>.slidingTag li:after {
    content: '';
    z-index: 3;
    height: 6px;
  }
  </code></pre>
  
  <p>I want to change the height attribute dynamically from JS. I can get the property using</p>
  
  <pre><code>window.getComputedStyle(document.querySelector('.slidingTag'), 'li:after').getPropertyValue('height')
  </code></pre>
  
  <p>But I do not know how to change the height attribute. I tried to use <code>setProperty</code> but it seems there is no such function available for pseudo-classes. Any ideas let me know. </p>