The following example shows how you can style the last button in a Flex ButtonBar control
by setting the lastButtonStyleName style.

<?xml version="1.0" encoding="utf-8"?>

<mx:Application name="ButtonBar_lastButtonStyleName_test"
        xmlns:mx="http://www.adobe.com/2006/mxml"
        layout="vertical"
        verticalAlign="middle"
        backgroundColor="white">

    <mx:Style>
        .lastButton {
            color: red;
            cornerRadius: 10;
            fontWeight: normal;
            themeColor: haloGreen;
        }
    </mx:Style>

    <mx:ButtonBar id="buttonBar"
            dataProvider="[Red,Orange,Yellow,Green,Blue]"
            lastButtonStyleName="lastButton" />

</mx:Application>

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