Flutter – how to make container to be almost in half of screen?

I have a question. Please see the image to understand better what I mean.

I want to create the yellow Containers like in the given image.

Here is my code:

import "package:flutter/material.dart";

void main(List<String> args) => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return const MaterialApp(
      home: Mypage(),
    );
  }
}

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

  @override
  State<Mypage> createState() => _MypageState();
}

class _MypageState extends State<Mypage> {
  TextEditingController height_controller = TextEditingController(text: '');

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.grey.shade800,
      appBar: AppBar(
        centerTitle: true,
        backgroundColor: Colors.grey.shade800,
        title: const Text(
          'BMI Calculator',
          style: TextStyle(color: Colors.amber),
        ),
      ),
   body: Padding(
        padding: const EdgeInsets.all(20.0),
        child: Column(
          children: [
            Row(
              children: [
                Align(
                  alignment: Alignment.topLeft,
                  child: SizedBox(
                    height: 150,
                    width: 150,
                    child: TextField(
                      controller: height_controller,
                      keyboardType: const TextInputType.numberWithOptions(),
                      decoration: const InputDecoration(
                        floatingLabelAlignment: FloatingLabelAlignment.center,
                        label: Text(
                          'Height',
                          style: TextStyle(color: Colors.amber, fontSize: 30),
                          textAlign: TextAlign.center,
                        ),
                      ),
                    ),
                  ),
                ),
                const SizedBox(
                  width: 70,
                ),
                const Align(
                  alignment: Alignment.topRight,
                  child: SizedBox(
                    height: 150,
                    width: 150,
                    child: TextField(
                      keyboardType: TextInputType.numberWithOptions(),
                      decoration: InputDecoration(
                        floatingLabelAlignment: FloatingLabelAlignment.center,
                        label: Text('Weight',
                            style:
                                TextStyle(color: Colors.amber, fontSize: 30)),
                      ),
                    ),
                  ),
                )
              ],
            ),
            TextButton(
              onPressed: () {},
              child: const Text(
                'Calculate',
                style: TextStyle(color: Colors.amber, fontSize: 30),
              ),
            ),
            const SizedBox(
              height: 300,
            ),
            Container(
              alignment: Alignment.center,
              height: 30,
              width: 300,
              decoration: BoxDecoration(
                  borderRadius: BorderRadius.circular(30), color: Colors.amber),
            ),
            const SizedBox(
              height: 30,
            ),
            Container(
              height: 30,
              width: 300,
              decoration: BoxDecoration(
                  borderRadius: BorderRadius.circular(30), color: Colors.amber),
            ),
          ],
        ),
      ),
    );
  }
}