title: Percentage Height HTML 5/CSS
body: <p>I am trying to set a <code>&lt;div&gt;</code> to a certain percentage height in CSS, but it just remains the same size as the content inside it. When I remove the HTML 5 <code>&lt;!DOCTYTPE html&gt;</code> however, it works, the <code>&lt;div&gt;</code> taking up the whole page as desired. I want the page to validate, so what should I do?</p>
  
  <p>I have this CSS on the <code>&lt;div&gt;</code>, which has an ID of <code>page</code>:</p>
  
  <pre><code>#page {
      padding: 10px;
      background-color: white;
      height: 90% !important;
  }
  </code></pre>