How do I get separate list item after .map in Flutter?

I’m new to Flutter and I have to make a list of rules where every item in the list is green and if you break a rule you can press it and change the color to red. I also have to have extensible.
I also have to have extensible. In my implementation from the YouTube tutorial, I saw that I used .map() to map the items in the list, but now when I have to press and change the color, all items change, not just one.

Any ideas how to fix this?

class _MyHomePageState extends State<MyHomePage> {

  bool isSelected = true;

  static const lawText =
      ' example text of the laws that are going to be implemented inside here. This is only to fill out the space at the moment';
  final List<Item> items = [
    Item(header: 'Law 1 ' , body: lawText),
    Item(header: 'Law 2 ' , body: lawText),
    Item(header: 'Law 3 ' , body: lawText),
    Item(header: 'Law 4 ' , body: lawText),
    Item(header: 'Law 5 ' , body: lawText),
  ];

  @override
  Widget build(BuildContext context) => Scaffold(
    drawer: NavBar(),
    appBar: AppBar(
      title: Text('§ Regel'),
      centerTitle: true,
    ),
    body: SingleChildScrollView(
      //crossAxisAlignment : crossAxisAlignment,
      child:ExpansionPanelList(
        expansionCallback: (index, isExpanded) {
          setState(() => items[index].isExpanded = !isExpanded);
        },
        children: items
            .map((item) => ExpansionPanel(
          isExpanded: item.isExpanded,
          headerBuilder:(context, isExpanded) => ListTile(
            tileColor: isSelected ? Colors.green : Colors.red,
            onTap:  () => setState(() => isSelected = !isSelected),
            shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.circular(20),
            ),
            title:Text(
              item.header,
              style: TextStyle(fontSize: 20),
            ),
          ),
          body: ListTile(
            title: Text(item.body, style: TextStyle(fontSize: 20) ),
            //tileColor: Colors.lightGreen,
            //onTap:  () => setState(() => isSelected = !isSelected),
          ),
        ))
            .toList(),
      ),
    ),
  );
}

class Item {
  final String header;
  final String body;
  bool isExpanded;

  Item({
    required this.header,
    required this.body,
    this.isExpanded = false,
  });
}

I try to do everything with ListTile instead of normal list.
I also tried using elementAt(index) but it didn’t work.