title: DIV height not work although have clear:both
body: <p>I have HTML and CSS below</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>.a{
   margin: 0px 150px;
   box-shadow: 0px 0px 10px #888888;
   text-align: center;
  }
  .a:before , .a:after{
   content: "";
   clear: both;
   visibility: hidden;
  }
  .b {
   float: left;
   width: 50%;
  }
  .c {
   float: right;
   width: 50%;</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="a"&gt;
   &lt;div class="b"&gt;
    &lt;ul&gt;
     &lt;li&gt;DATA 1&lt;/li&gt;
     &lt;li&gt;DATA 1&lt;/li&gt;
     &lt;li&gt;DATA 1&lt;/li&gt;
    &lt;/ul&gt;
   &lt;/div&gt;
   &lt;div class="c"&gt;
    &lt;ul&gt;
     &lt;li&gt;DATA 1&lt;/li&gt;
     &lt;li&gt;DATA 1&lt;/li&gt;
     &lt;li&gt;DATA 1&lt;/li&gt;
    &lt;/ul&gt;
   &lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>But <code>&lt;div class="a"&gt;</code> not surrounded 2 <code>&lt;div class="b"&gt;</code> and <code>&lt;div class="c"&gt;</code> although I was add clear:both ?</p>
  
  <p>Now I must add height for div.a to solve this problem but I don't want this.</p>
  
  <p><img src="https://i.stack.imgur.com/utnlt.png" alt="enter image description here"></p>
  
  <p>Why and how to fix this ?</p>
  
  <p>Thanks you so much</p>