Step1: Add get under dependencies in pubspec.yaml file:

                           get:
                        

Step2 :Import get in main.dart

                        import 'package:get/get.dart';
                        

Step 3: dialog

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

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

                        class MyApp extends StatelessWidget {

                        // This widget is the root of your application.
                        @override
                        Widget build(BuildContext context) {
                          return GetMaterialApp(
                          title: 'Dialog Demo',
                          theme: ThemeData(
                            primarySwatch: Colors.blue,
                          ),
                          home: Home(),
                          debugShowCheckedModeBanner: false,
                          );
                        }
                        }

                        class Home extends StatelessWidget {
                        @override
                        Widget build(BuildContext context) {
                          return Scaffold(
                          appBar: AppBar(
                            title: Text('GeeksforGeeks Dialog'),
                            centerTitle: true,
                            backgroundColor: Colors.green,
                          ),
                          body: Center(
                            child: ElevatedButton(
                            child: Text('Show Dialog'),
                            onPressed: (){
                              Get.defaultDialog(

                              );
                            },
                            )
                          ),
                          );
                        }
                        }
                      

Additional parameters

                      Get.defaultDialog(
                      title: "GeeksforGeeks",
                      middleText: "Hello world!",
                      backgroundColor: Colors.green,
                      titleStyle: TextStyle(color: Colors.white),
                      middleTextStyle: TextStyle(color: Colors.white),
                      textConfirm: "Confirm",
                      textCancel: "Cancel",
                      cancelTextColor: Colors.white,
                      confirmTextColor: Colors.white,
                      buttonColor: Colors.red,
                      barrierDismissible: false,
                      radius: 50,
                      content: Column(
                        children: [
                          Container(child:Text("Hello 1")),
                          Container(child:Text("Hello 2")),
                          Container(child:Text("Hello 3")),
                        ],
                      )
                    );