title: How to set :focus background color on the button
body: <p>My problem so little but I am very confused where I am going wrong.</p>
  
  <p>I can not set the <code>:focus</code> background color on my button. </p>
  
  <p><strong>My css</strong></p>
  
  <pre><code>span {background: #000; display:inline-block; padding: 13px 1% 7px; text-align: center; width: 50px; cursor:pointer}
  label {background: #fff; display: inline-block; height: 3px; margin: 0 0 5px; vertical-align: middle; width: 100%; cursor:pointer}
  span:hover label{background:red;}
  span:active label{background:green;}
  span:focus label{background:#0ff;}
  </code></pre>
  
  <p>and my HTML</p>
  
  <pre><code>&lt;span id="open"&gt;
   &lt;label&gt;&lt;/label&gt;
   &lt;label&gt;&lt;/label&gt;
   &lt;label&gt;&lt;/label&gt;
  &lt;/span&gt;
  </code></pre>
  
  <p>Please tell me where I going wrong. </p>