How to make transparent background of Silverlight 3 application?-Collection of common programming errors

How to make transparent background of Silverlight 3 application? I have the next code but it does not work (

          
          
          
BGtest

html, body {
    height: 100%;
    overflow: auto;
}
body {

    padding: 0;
    margin: 0;
}
#silverlightControlHost {
    height: 100%;
    text-align:center;
}



    function onSilverlightError(sender, args) {
        var appSource = "";
        if (sender != null && sender != 0) {
          appSource = sender.getHost().Source;
        }

        var errorType = args.ErrorType;
        var iErrorCode = args.ErrorCode;

        if (errorType == "ImageError" || errorType == "MediaError") {
          return;
        }

        var errMsg = "Unhandled Error in Silverlight Application " +  appSource + "\n" ;

        errMsg += "Code: "+ iErrorCode + "    \n";
        errMsg += "Category: " + errorType + "       \n";
        errMsg += "Message: " + args.ErrorMessage + "     \n";

        if (errorType == "ParserError") {
            errMsg += "File: " + args.xamlFile + "     \n";
            errMsg += "Line: " + args.lineNumber + "     \n";
            errMsg += "Position: " + args.charPosition + "     \n";
        }
        else if (errorType == "RuntimeError") {           
            if (args.lineNumber != 0) {
                errMsg += "Line: " + args.lineNumber + "     \n";
                errMsg += "Position: " +  args.charPosition + "     \n";
            }
            errMsg += "MethodName: " + args.methodName + "     \n";
        }

        throw new Error(errMsg);
    }