I was writing Flutter code using flexible, and something happened that I didn't understand

I’m making a Pomodoro app. I’m configuring the screen as flexible, but the flexible one with the iconbutton doesn’t seem to be working properly. It will look like the picture.

import 'dart:async';
import 'package:flutter/material.dart';

class HomeScreen extends StatefulWidget {
  const HomeScreen({super.key});

  @override
  State<HomeScreen> createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  static const twentyFiveMinutes = 1500;
  int totalSeconds = twentyFiveMinutes;
  bool isRunning = false;
  int totalPomodoro = 0;
  late Timer timer;

  void onTick(Timer timer) {
    if (totalSeconds == 0) {
      setState(() {
        totalPomodoro = totalPomodoro + 1;
        isRunning = false;
        totalSeconds = twentyFiveMinutes;
      });
      timer.cancel();
    } else {
      setState(() {
        totalSeconds = totalSeconds - 1;
      });
    }
  }
  void onStartPressed() {
    timer = Timer.periodic(const Duration(seconds: 1), onTick);

    setState(() {
      isRunning = true;
    });
  }

  void onPausePressed() {
    timer.cancel();

    setState(() {
      isRunning = false;
    });
  }

  void onResetPressed() {
    setState(() {
      totalSeconds = twentyFiveMinutes;
      isRunning = false;
      timer.cancel();
    });
  }

  String format(int seconds) {
    var duration = Duration(seconds: seconds);
    return duration.toString().split('.').first.substring(2);
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: isRunning
          ? Theme.of(context).secondaryHeaderColor
          : Theme.of(context).colorScheme.background,
      body: Column(
        children: [
          Flexible(
            flex: 1,
            child: Container(
              alignment: Alignment.bottomCenter,
              child: Text(
                format(totalSeconds),
                style: TextStyle(
                  color: Theme.of(context).cardColor,
                  fontSize: 89,
                  fontWeight: FontWeight.w600,
                ),
              ),
            ),
          ),
          Flexible(
            flex: 3,
            child: Row(
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: [
                IconButton(
                  iconSize: 120,
                  color: Theme.of(context).cardColor,
                  onPressed: isRunning ? onPausePressed : onStartPressed,
                  icon: Icon(
                    isRunning
                        ? Icons.pause_circle_outline
                        : Icons.play_circle_outline,
                  ),
                ),
                IconButton(
                    iconSize: 120,
                    color: Theme.of(context).cardColor,
                    onPressed: onResetPressed,
                    icon: const Icon(Icons.rotate_left_sharp))
              ],
            ),
          ),
          Flexible(
            flex: 1,
            child: Row(
              children: [
                Expanded(
                  child: Container(
                    decoration: BoxDecoration(
                      color: Theme.of(context).cardColor,
                      borderRadius:
                          const BorderRadius.vertical(top: Radius.circular(50)),
                    ),
                    child: Column(
                      mainAxisAlignment: MainAxisAlignment.center,
                      children: [
                        Text(
                          'Pomodoros',
                          style: TextStyle(
                            fontSize: 20,
                            fontWeight: FontWeight.w600,
                            color:
                                Theme.of(context).textTheme.displayLarge!.color,
                          ),
                        ),
                        Text(
                          '$totalPomodoro',
                          style: TextStyle(
                            fontSize: 58,
                            fontWeight: FontWeight.w600,
                            color:
                                Theme.of(context).textTheme.displayLarge!.color,
                          ),
                        ),
                      ],
                    ),
                  ),
                ),
              ],
            ),
          ),
        ],
      ),
    );
  }
}

I tried changing the value of flex, but only the flexible with the iconbutton does not change in size.