title: content property in CSS
body: <p>In some template I see that an arrow that created with CSS. something like this:</p>
  
  <pre><code>div:after{
      content:"\f107";
  }
  </code></pre>
  
  <p>this code display an arrow like  this :</p>
  
  <p><img src="https://i.stack.imgur.com/10QVE.jpg" alt="enter image description here"></p>
  
  <p>what is this code? where I can find more codes?</p>