size property
Customizes the marker size. This value is applied for both the width and height of the marker.
Defaults to 5.
@override
Widget build(BuildContext context) {
 return Scaffold(
   body: Center(
       child: SfSparkAreaChart(
     marker: SparkChartMarker(
         size: 20)
        )
     ),
  );
}
Implementation
final double size;