title: 'hidden' property does not work with flex-box
body: <p>I have the following code using flex-box</p>
  
  <pre><code>  &lt;!DOCTYPE html&gt;
  
    &lt;polymer-element name='test-flex'&gt;
      &lt;template&gt;
  
        &lt;style&gt;
           .lab-flex-col-container {
             display: flex;
             flex-flow: column;
             align-content: center;
             background-color: gold;
             border-radius:5px;
             margin: 5px;
          }
  
          .lab-flex-col {
            display:flex;
            flex-flow:column;
            align-self:center;
            margin:5px;
          }
  
          .margin2 { margin: 2px; }
  
  
        &lt;/style&gt;
  
        &lt;form id='form'
          class='form'&gt;
  
          &lt;div class='lab-flex-col-container'&gt;
             &lt;div class='lab-flex-col' id='hidden-does-not-work' hidden&gt;
                &lt;input id='hidden-works' type='text'&gt;
             &lt;/div&gt;
  
             &lt;div id='hidden-works' hidden&gt;
                &lt;textarea&gt;&lt;/textarea&gt;
             &lt;/div&gt;
             &lt;div id='hidden-does-not-work-here-either' class='lab-flex-col' hidden&gt;
                &lt;button&gt;Save&lt;/button&gt;
             &lt;/div&gt;
  
          &lt;/div&gt;
        &lt;/form&gt;
  
      &lt;/template&gt;
  
      &lt;script type="application/dart;component=1"&gt;
  
        import 'package:polymer/polymer.dart';
        import 'dart:html';
  
  
        @CustomTag( 'test-flex' )
        class TestFlex extends PolymerElement
        {
  
          TestFlex.created() : super.created();
  
          ready()
          {
            $['hidden-does-not-work'].hidden = true;
          }
  
          void syncDb ( Event e, var detail, var target )
          {
  
          }
  
          @override
          void enteredView()
          {
             super.enteredView();
  
             $['hidden-does-not-work-here-either'].hidden = true;
  
          }
        }
  
      &lt;/script&gt;
    &lt;/polymer-element&gt;
  </code></pre>
  
  <p>Why does the presence of the lab-flex-col class prevents the hiding of the text input?
  I have tried hidden='hidden' and this does not work either.</p>
  
  <p>When hidden is present as in the textarea element, it works as expected, but once the flex-box class is added, it ceases to work and the element remains visible.</p>