<?xml version="1.0" encoding="utf-8"?>
<!-- http://blog.flexexamples.com/2008/05/24/setting-the-focus-thickness-on-a-numericstepper-control-in-flex/ -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Style>
        NumericStepper {
            focusThickness: 10;
        }
    </mx:Style>

    <mx:ApplicationControlBar dock="true">
        <mx:Button id="btn"
                label="click here to remove focus" />
    </mx:ApplicationControlBar>

    <mx:Form>
        <mx:FormItem label="focusThickness:">
            <mx:NumericStepper id="numericStepper"
                    minimum="0"
                    maximum="10" />
        </mx:FormItem>
    </mx:Form>

</mx:Application>