Dialog fixed positioning below TextButton

Question

How do I achieve this design? "Filter by" is a button on which this start and end date dialog is opened. But not able exactly open this at the same position on different devices as this design.

This is what I have tried:

filterDialog(BuildContext context) {
    return Center(
      child: Container(
        margin: EdgeInsets.only(left: 30, top: Get.height \* 0.06),
        width: 330,
        height: 65,
        decoration: BoxDecoration(
          boxShadow: [
            BoxShadow(
                color: Colors.grey.shade400,
                blurRadius: 5,
                spreadRadius: 1
            )
          ],
          borderRadius: BorderRadius.circular(5),
        ),
        clipBehavior: Clip.antiAlias,
        child: Scaffold(
          body: Row(
            mainAxisAlignment: MainAxisAlignment.center,
            children: [
              GestureDetector(
                onTap: () {
                  _datePicker(context, true);
                },
                child: Container(
                  width: 150,
                  height: 40,
                  margin: const EdgeInsets.only(top: 12, right: 7),
                  child: TextFormField(
                    enabled: false,
                    controller: controller.startDateTec,
                    style: const TextStyle(color: AppConstants.appThemeColor, fontSize: 12, fontFamily: AppConstants.robotoRegular),
                    decoration: AppWidgets.calendarTextField("Start Date"),
                  ),
                ),
              ),
              GestureDetector(
                onTap: () {
                  _datePicker(context, false);
                },
                child: Container(
                  width: 150,
                  height: 40,
                  margin: const EdgeInsets.only(top: 12, right: 7),
                  child: TextFormField(
                    enabled: false,
                    controller: controller.endDateTec,
                    style: const TextStyle(color: AppConstants.appThemeColor, fontSize: 12, fontFamily: AppConstants.robotoRegular),
                    decoration: AppWidgets.calendarTextField("End Date"),
                  ),
                ),
              )
            ],
          ),
        ),
      ),
    );
  }

What changes can be done? Or else any other widget instead of dialog needs to be used?