tickPosition property
Position of the tick lines.
Tick lines can be placed either inside or outside the plot area.
Defaults to TickPosition.outside.
Also refer TickPosition.
Widget build(BuildContext context) {
    return Container(
        child: SfCartesianChart(
           primaryXAxis: NumericAxis(tickPosition: TickPosition.inside),
        )
    );
}
Implementation
final TickPosition tickPosition;