DecoratedBoxTransition sample code (#63775)

packages/flutter/lib/src/widgets/transitions.dart

@@ -899,6 +899,74 @@ class RelativePositionedTransition extends AnimatedWidget {
 /// [decoration] animated by a [CurvedAnimation] set to [Curves.decelerate]:
 /// {@animation 300 378 https://flutter.github.io/assets-for-api-docs/assets/widgets/decorated_box_transition.mp4}
 ///
+/// {@tool dartpad --template=stateful_widget_material_ticker}
+/// The following code implements the [DecoratedBoxTransition] as seen in the video
+/// above:
+///
+/// ```dart
+/// final DecorationTween decorationTween = DecorationTween(
+///   begin: BoxDecoration(
+///     color: const Color(0xFFFFFFFF),
+///     border: Border.all(style: BorderStyle.none),
+///     borderRadius: BorderRadius.circular(60.0),
+///     shape: BoxShape.rectangle,
+///     boxShadow: const <BoxShadow>[
+///       BoxShadow(
+///         color: Color(0x66666666),
+///         blurRadius: 10.0,
+///         spreadRadius: 3.0,
+///         offset: Offset(0, 6.0),
+///       )
+///     ],
+///   ),
+///   end: BoxDecoration(
+///     color: const Color(0xFFFFFFFF),
+///     border: Border.all(
+///       style: BorderStyle.none,
+///     ),
+///     borderRadius: BorderRadius.zero,
+///     // No shadow.
+///   ),
+/// );
+///
+/// AnimationController _controller;
+///
+/// @override
+/// void initState() {
+///   _controller = AnimationController(
+///     vsync: this,
+///     duration: const Duration(seconds: 3),
+///   )..repeat(reverse: true);
+///   super.initState();
+/// }
+///
+/// @override
+/// void dispose() {
+///   _controller.dispose();
+///   super.dispose();
+/// }
+///
+///  @override
+///  Widget build(BuildContext context) {
+///    return Container(
+///      color: Colors.white,
+///      child: Center(
+///        child: DecoratedBoxTransition(
+///          position: DecorationPosition.background,
+///          decoration: decorationTween.animate(_controller),
+///          child: Container(
+///            width: 200,
+///            height: 200,
+///            padding: const EdgeInsets.all(10),
+///            child: const FlutterLogo(),
+///          ),
+///        ),
+///      ),
+///    );
+///  }
+/// ```
+/// {@end-tool}
+///
 /// See also:
 ///
 ///  * [DecoratedBox], which also draws a [Decoration] but is not animated.