Flex VBox and HBox containers

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
backgroundColor="#FFFFFF" backgroundAlpha="0">
<mx:VBox horizontalAlign="center" verticalGap="15">
<mx:HBox verticalAlign="middle" horizontalGap="15">
<mx:Button label="&lt; prev" left="10" top="120" />
<mx:Image source="assets/animals03.jpg"
horizontalCenter="0" top="30"/>
<mx:Button label="next &gt;" right="10" top="120"/>
</mx:HBox>
<mx:Label text="Photographed by Elsie Weil"
horizontalCenter="0" top="250"/>
</mx:VBox>
</mx:Application>