title: What does the CSS pseudo selector :after do other than set content?
body: <p>Can someone explain what this code from Bootstrap is doing?</p>
  
  <pre><code>*:before,
  *:after {
    -webkit-box-sizing: border-box;
    -moz-box-sizing: border-box;
    box-sizing: border-box; }
  </code></pre>
  
  <p>I understand the box-sizing part.</p>
  
  <p>I think I understand *:after. However I am familiar with this usage:</p>
  
  <pre><code>*:after {
    content: 'hello world'
  }
  </code></pre>
  
  <p>In the case without a content property what is this doing? Is it saying "all elements inserted with :after should also have box-sizing 'border-box'" - or something else?</p>