title: Position fixed 100 of parent
body: <p>I'm in difficulty: I have a parent element that has a size that doesn't know. And I have an item that it must place permanently at the top of the body, then <code>position: fixed</code>, but I cann't because giving it <code>width: 100%</code>, is 100% of the body, but I want 100% of the parent element. How can I do?</p>
  
  <p>Example: <a href="http://codepen.io/michele96/pen/jWbYQb" rel="noreferrer">http://codepen.io/michele96/pen/jWbYQb</a></p>