title: why the class margin not work?
body: <p>The code is as below:</p>
  
  <pre><code>&lt;html&gt;
  &lt;head&gt;
  &lt;title&gt;test&lt;/title&gt;
  &lt;/head&gt;
  &lt;body&gt;
  &lt;div&gt;&lt;span&gt;shanghai&lt;/span&gt;&lt;span class="margin"&gt; &lt;/span&gt;&lt;span&gt;male&lt;/span&gt;&lt;/div&gt;
  &lt;/body&gt;
  &lt;/html&gt;
  
  .margin {
      width:40px;
      height:auto;
  }
  </code></pre>