<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/05/21/aligning-a-label-in-a-button-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white" viewSourceURL="srcview/index.html">

    <mx:Script>
        <![CDATA[
            import mx.events.ItemClickEvent;

            private function toggleButtonBar_itemClick(evt:ItemClickEvent):void {
                button.setStyle("textAlign", evt.item.label);
            }
        ]]>
    </mx:Script>

    <mx:Array id="arr">
        <mx:Object label="left" />
        <mx:Object label="center" />
        <mx:Object label="right" />
    </mx:Array>

    <mx:ApplicationControlBar dock="true">
        <mx:Form styleName="plain">
            <mx:FormItem label="textAlign:">
                <mx:ToggleButtonBar id="toggleButtonBar"
                        dataProvider="{arr}"
                        selectedIndex="1"
                        itemClick="toggleButtonBar_itemClick(event);" />
            </mx:FormItem>
        </mx:Form>
    </mx:ApplicationControlBar>

    <mx:Button id="button"
            label="Button"
            textAlign="center"
            width="200" />

</mx:Application>