title: Why does making window background transparent mess up the layout?
body: <p>I was able to make the window background transparent with baseCls, but then the layout is messed up.</p>
  
  <p>How to avoid that?</p>
  
  <pre><code>.myclass .x-window {
      background-color: rgba(1, 1, 1, 1);
  }
  
  Ext.onReady(function() {
      Ext.create('Ext.window.Window', {
          title: 'Hello',
          height: 400,
          itemId: 'mywin',
          width: 600,
          baseCls: 'myclass',
          items: [{
              xtype: 'button',
              text: 'Show MessageBox',
              listeners: {
                  click: function() {                
                      Ext.Msg.prompt('Name', 'Please enter your name:', function(btn, text){
                          if (btn == 'ok'){
                              // process text value and close...
                          }
                      });
                  }
              }
          }]
      }).show();
  });
  </code></pre>