title: How do I set Extjs panel's layouts to fit to whole page?
body: <p>I'm developing a web application with <a href="http://docs.sencha.com/extjs/6.0/" rel="nofollow">Extjs 6</a> in client side. In first level of my page, I have a panel(panel_a). <strong>I want to this panel fit to the whole page</strong>.   </p>
  
  <p>In this panel I have another panel(panel_b). <strong>I want to fit this panel in panel_a too</strong>.</p>
  
  <p>How do I set the panel's layouts?</p>