Opacity (Container) with Slider Simple Example

 import "package:flutter/material.dart";

void main() {
  runApp(const MyApp());
}

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

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: "Opacity Example",
      debugShowCheckedModeBanner: false,
      theme: ThemeData(
        primarySwatch: Colors.grey,
      ),
      home: const OpacityExample(),
    );
  }
}

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

  @override
  State<OpacityExample> createState() {
    return OpacityExampleState();
  }
}

class OpacityExampleState extends State<OpacityExample> {
  double opacity = 0.4;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("Opacity Example"),
        centerTitle: true,
        backgroundColor: Colors.grey,
      ),
      body: Column(
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          Container(
            width: 200.0,
            height: 200.0,
            color: Colors.brown.withOpacity(opacity),
          ),
          const SizedBox(height: 50.0),
          Slider(
            value: opacity,
            onChanged: (value) {
              print(value);
              opacity = value;
              setState(() {});
            },
          ),
        ],
      ),
    );
  }
}