title: width: 100% making things go out of the div
body: <p>I have a simple div in which I have 2 textarea. I set the textarea's width to <code>100%</code> but then it just go a little out of the div.</p>
  
  <p>See this <a href="http://jsfiddle.net/YE5MP/" rel="nofollow">fiddle</a>.</p>
  
  <p><strong>HTML:</strong></p>
  
  <pre><code>&lt;div class="offer_a_help"&gt;
      &lt;textarea&gt;&lt;/textarea&gt;
      &lt;br/&gt;
      &lt;textarea&gt;&lt;/textarea&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p><strong>CSS:</strong></p>
  
  <pre><code>.offer_a_help {
      width: 350px;
      height: 250px;
      position: absolute;
      top: calc(100%/2 - 350px/2);
      left: calc(100%/2 - 250px/2);
      background-color: #eee;
      border-radius: 5px;
      border: 1px solid #bbb;
  }
  .offer_a_help textarea {
      width: 100%;
  }
  </code></pre>
  
  <p>Why is that happening and what's the simplest way to fix this?</p>