PageController's viewportFraction property is set to less than 1, and there is a bounce when switching pages.

main.dart

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(home: HomePage());
  }
}

class HomePage extends StatefulWidget {
  @override
  _HomePageState createState() => _HomePageState();
}

class _HomePageState extends State<HomePage> {
  PageController controller = PageController(viewportFraction: 0.8);
  @override
  Widget build(BuildContext context) {
    var colors = [Colors.green, Colors.orange, Colors.purple];
    return Scaffold(
      appBar: AppBar(
        title: Text('Home Page'),
      ),
      body: Center(
        child: PageView(
          controller: controller,
          children: <Widget>[
            for (var color in colors)
              Container(
                color: color,
              )
          ],
        ),
      ),
    );
  }
}