package {
	import flash.display.Sprite;
	import flash.events.Event;
	import flash.net.URLLoader;
	import flash.net.URLRequest;
	import flash.text.StyleSheet;
	import flash.text.TextField;
	import flash.text.TextFieldAutoSize;

	public class CSSFormattingExample extends Sprite {
		var loader:URLLoader;
		var field:TextField;
		var exampleText:String = "<h1>This is a headline</h1>" +
		"<p>This is a line of text. <span class='bluetext'>" +
		"This line of text is colored blue.</span></p>";

		public function CSSFormattingExample():void {
			field = new TextField();
			field.width=300;
			field.autoSize=TextFieldAutoSize.LEFT;
			field.wordWrap=true;
			addChild(field);

			var req:URLRequest=new URLRequest("example.css");

			loader = new URLLoader();
			loader.addEventListener(Event.COMPLETE, onCSSFileLoaded);
			loader.load(req);
		}

		public function onCSSFileLoaded(event:Event):void {
			var sheet:StyleSheet = new StyleSheet();
			sheet.parseCSS(loader.data);
			field.styleSheet=sheet;
			field.htmlText=exampleText;
		}
	}
}


// THE 'example.css' FILE SHOULD LOOK LIKE THIS ...
//p {
//	font-family: Times New Roman, Times, _serif;
//	font-size: 14;
//}
//
//h1 {
//	font-family: Arial, Helvetica, _sans;
//	font-size: 20;
//	font-weight: bold;
//}
//
//.bluetext {
//	color: #0000CC;
//}

http://livedocs.adobe.com/flash/9.0/main/wwhelp/wwhimpl/common/html/wwhelp.htm?context=LiveDocs_Parts&file=00000232.html

AS3 Loading and Using an External CSS File

css, format, text

ActionScript 3