# Root Widget

All stories are wrapped in an root widget (i.e. an `App` widget) to provide a context for the stories to render in.

```tree
RootWidget
└── Addon 1
  └── Addon 2
    └── Story
```

You can use a custom root widget by providing an `appBuilder` function to the `Config`.
This is helpful if you need to wrap your app widget (i.e. `MaterialApp`, `CupertinoApp`) with another custom widget.

<Info>
  If you want to wrap your story in a custom widget, you can also use the
  [Addons API](/addons/overview), which provides some more flexibility.
</Info>

```dart title=widgetbook/lib/widgetbook.config.dart
// Material App (default)
final config = Config(
  // ...
  appBuilder: materialAppBuilder,
);

// Cupertino App
final config = Config(
  // ...
  appBuilder: cupertinoAppBuilder,
);

// Custom App
final config = Config(
  // ...
  appBuilder: (context, child) {
    return MyCustomAppWidget(
      child: child,
    );
  },
);
```