mustella/Assets/Components/TrixSparkButton.mxml

<?xml version="1.0" encoding="utf-8"?>
<s:Button 
    xmlns:fx="http://ns.adobe.com/mxml/2009" 
    xmlns:mx="library://ns.adobe.com/flex/mx" 
    xmlns:s="library://ns.adobe.com/flex/spark"
	width="150" 
	height="30"
    label="My Spark Button">
</s:Button>