style property

The text style to use for text in the combo box button and the combo box menu that appears when you tap the button.

To use a separate text style for selected item when it's displayed within the combo box button, consider using selectedItemBuilder.

This sample shows a ComboBox with a combo box button text style that is different than its menu items.

List<String> options = <String>['One', 'Two', 'Free', 'Four'];
String comboboxValue = 'One';

@override
Widget build(BuildContext context) {
  return Container(
    alignment: AlignmentDirectional.center,
    color: Colors.blue,
    child: ComboBox<String>(
      value: comboboxValue,
      onChanged: (String? newValue) {
        setState(() {
          comboboxValue = newValue!;
        });
      },
      style: TextStyle(color: Colors.blue),
      selectedItemBuilder: (BuildContext context) {
        return options.map((String value) {
          return Text(
            comboboxValue,
            style: TextStyle(color: Colors.white),
          );
        }).toList();
      },
      items: options.map<ComboBoxItem<String>>((String value) {
        return ComboBoxItem<String>(
          value: value,
          child: Text(value),
        );
      }).toList(),
    ),
  );
}

Defaults to the Typography.body value of the closest FluentThemeData