Customizing a Flex ToolTip instance’s appearance using styles

<?xml version="1.0" encoding="utf-8"?>
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml"
                creationComplete="init();">
 
    <mx:Style>
        ToolTip {
            backgroundColor: black;
            backgroundAlpha: 1.0;
            cornerRadius: 0;
            color: white;
        }
    </mx:Style>
 
    <mx:Script>
        <![CDATA[
            private var btn2:Button;
 
            private function init():void {
                btn2 = new Button();
                btn2.label = "AS button w/ AS toolTip";
                btn2.toolTip = "Foo bar 2";
                addChild(btn2);
            }
        ]]>
    </mx:Script>
 
    <mx:Button label="Roll over to see tool tip"
               toolTip="The quick brown fox jumped over the lazy dog." />
    <mx:Button id="btn" label="MXML button w/ AS toolTip" creationComplete="btn.toolTip = 'Foo bar';" />
 
</mx:Application>