title: background image for an <a> tag
body: <p>please help me. I can't understand why my css code for background image doesn't work.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.fb {
      margin-bottom: 10px;
      width: 160px;
      height:160px;
      display:block;
      background:transparent url('/images/social%20icons/normal/fb.png') center top no-repeat;
  }
  
  .fb:hover {
      background-image: url('/images/social%20icons/hover/fb.png');
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;a href="#" class="fb"&gt;&lt;/a&gt;</code></pre>
  </div>
  </div>
  
  <a href="https://i.stack.imgur.com/WAgGS.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/WAgGS.png" alt="enter image description here"></a></p>