AppBallon.dart

import 'package:flutter/material.dart';
import 'dart:math' as math;

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(

        primarySwatch: Colors.blue,
      ),
      home: HomeWidget(),
    );
  }
}


class HomeWidget extends StatefulWidget {
  @override
  _HomeWidgetState createState() => _HomeWidgetState();
}

class _HomeWidgetState extends State<HomeWidget> {
  @override
  Widget build(BuildContext context) {
    return Material(
      child: Center(
        child: BalloonWidget(
          height: 80,
          width: 200,
          color: Colors.grey[800],
          child: Row(
            children: <Widget>[
              IconButton(icon: Icon(Icons.home, color: Colors.white,), onPressed: () {},),
              IconButton(icon: Icon(Icons.share, color: Colors.white,), onPressed: () {},),
              IconButton(icon: Icon(Icons.keyboard, color: Colors.white,), onPressed: () {},),
              Padding(
                padding: const EdgeInsets.symmetric(vertical: 14),
                child: Container(height: double.infinity, width: 1, color: Colors.white,),
              ),
              IconButton(icon: Icon(Icons.palette, color: Colors.white,), onPressed: () {},),
   
            ],
          ),
        ),
      ),
    );
  }
}


//widget que faz o balao
class BalloonWidget extends StatelessWidget {
  final double height;
  final double width;
  final Color color;
  final Widget child;

  const BalloonWidget({Key key, this.height, this.width, this.child, this.color})
      : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      height: height,
      width: width,
      child: Stack(
        children: <Widget>[
          Container(
            decoration: BoxDecoration(
              color: color,
              borderRadius: BorderRadius.circular(12),
            ),
            width: width,
            height: height * 0.8,
            child: child,
          ),
          Align(
            alignment: Alignment.bottomCenter,
            child: Transform.rotate(
              angle: math.pi * 0.25,
              child: Container(
                color: color,
                height: (height * 0.8) / 2,
                width: (height * 0.8) / 2,
              ),
            ),
          )
        ],
      ),
    );
  }
}