How can I solve a problem with the "Checkbox" icon?

main.dart

import 'package:flutter/material.dart';

void main() => runApp(const MaterialApp(home: ToDo()));

class ToDo extends StatelessWidget {
  const ToDo({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: const Text("To-Do-App"),
          backgroundColor: const Color.fromRGBO(35, 152, 185, 100),
        ),
        body: Column(
          children: const <Widget>[
            ToDoItem("Tomate"),
            ToDoItem("Käse"),
            ToDoItem("Lauch"),
            ToDoItem("Paprika"),
            ToDoItem("Wein"),
          ],
        ));
  }
}

class ToDoItem extends StatefulWidget {
  final String title;

  const ToDoItem(
    this.title, {
    Key? key,
  }) : super(key: key);

  @override
  State<ToDoItem> createState() => _ToDoItemState();
}

class _ToDoItemState extends State<ToDoItem> {
  bool isChecked = false;

  @override
  Widget build(BuildContext context) {
    return Container(
      padding: const EdgeInsets.symmetric(horizontal: 22),
      child: ListTile(
        contentPadding: const EdgeInsets.symmetric(vertical: 8.0),
        leading: Checkbox(
          onChanged: (bool? value) {
            setState(() {
              isChecked = !isChecked;
            });
          },
          value: isChecked,
        ),
        title: Text(
          widget.title,
          style: const TextStyle(
              fontSize: 18.0,
              fontWeight: FontWeight.w600,
              color: Colors.black54),
        ),
        trailing: const Icon(Icons.delete_outline),
      ),
    );
  }
}