Flutter: Change color of every modalBottomSheet within the darkTheme ThemeData options?

Question

I have this code for my dark mode color theme. And I want to changed the color of all modalBottomSheets globally using this code. However I can't figure out what I use to change that part of the theme.

var kDarkColorScheme = ColorScheme.fromSeed(seedColor: Colors.grey);
void main() {
  runApp(
    MaterialApp(
      darkTheme: ThemeData.dark().copyWith(
        useMaterial3: true,
        colorScheme: kDarkColorScheme,
        cardTheme: CardTheme().copyWith(
          color: kDarkColorScheme.secondaryContainer,
          margin: EdgeInsets.symmetric(
            horizontal: 16, 
            vertical: 8),
          ),
          appBarTheme: AppBarTheme().copyWith(
            backgroundColor: Color.fromARGB(137, 0, 0, 0),
            foregroundColor: Color.fromARGB(255, 122, 122, 122),
          ),
          
          
      ),

This is my modalBottomSheet's code:

  void _openAddExpenseOverlay() {
    showModalBottomSheet(
      isScrollControlled: true,
      context: context,
      builder: (ctx) => NewExpense(onAddExpense: _addExpense),
    );
  }

I tried adding popupMenuTheme: PopupMenuThemeData(color: Colors.red), to the ThemeData. However this doesn't change anything on my modalBottomSheet. I know I need to set something that's same type of value in the same place I set this popupMenuTheme: There is no modalBottomSheet: on the autofill list though. Sorry if this last bit is confusing, I'm only in the beginning of learning flutter and I don't remember the names of stuff well (What is it? parameter, operator, function, idk I get these words mixed up).