Use PageTheme in example

@@ -5,6 +5,7 @@
 - Simplify iOS code
 - Improve native code
 - Add Printing.info()
+- Use PageTheme in example
 
 ## 2.1.9
 

@@ -18,12 +18,10 @@ Future<Document> generateDocument(PdfPageFormat format) async {
         print('Unable to download image');
       });
 
-  pdf.addPage(MyPage(
-    pageFormat: format.applyMargin(
-        left: 2.0 * PdfPageFormat.cm,
-        top: 4.0 * PdfPageFormat.cm,
-        right: 2.0 * PdfPageFormat.cm,
-        bottom: 2.0 * PdfPageFormat.cm),
+  final PageTheme pageTheme = myPageTheme(format);
+
+  pdf.addPage(Page(
+    pageTheme: pageTheme,
     build: (Context context) => Row(children: <Widget>[
       Expanded(
           child: Column(

@@ -6,48 +6,54 @@ import 'package:qr/qr.dart';
 const PdfColor green = PdfColor.fromInt(0xff9ce5d0);
 const PdfColor lightGreen = PdfColor.fromInt(0xffcdf1e7);
 
-class MyPage extends Page {
-  MyPage(
-      {PdfPageFormat pageFormat = PdfPageFormat.a4,
-      BuildCallback build,
-      EdgeInsets margin})
-      : super(pageFormat: pageFormat, margin: margin, build: build);
-
-  @override
-  void paint(Widget child, Context context) {
-    context.canvas
-      ..setColor(lightGreen)
-      ..moveTo(0, pageFormat.height)
-      ..lineTo(0, pageFormat.height - 230)
-      ..lineTo(60, pageFormat.height)
-      ..fillPath()
-      ..setColor(green)
-      ..moveTo(0, pageFormat.height)
-      ..lineTo(0, pageFormat.height - 100)
-      ..lineTo(100, pageFormat.height)
-      ..fillPath()
-      ..setColor(lightGreen)
-      ..moveTo(30, pageFormat.height)
-      ..lineTo(110, pageFormat.height - 50)
-      ..lineTo(150, pageFormat.height)
-      ..fillPath()
-      ..moveTo(pageFormat.width, 0)
-      ..lineTo(pageFormat.width, 230)
-      ..lineTo(pageFormat.width - 60, 0)
-      ..fillPath()
-      ..setColor(green)
-      ..moveTo(pageFormat.width, 0)
-      ..lineTo(pageFormat.width, 100)
-      ..lineTo(pageFormat.width - 100, 0)
-      ..fillPath()
-      ..setColor(lightGreen)
-      ..moveTo(pageFormat.width - 30, 0)
-      ..lineTo(pageFormat.width - 110, 50)
-      ..lineTo(pageFormat.width - 150, 0)
-      ..fillPath();
-
-    super.paint(child, context);
-  }
+PageTheme myPageTheme(PdfPageFormat format) {
+  return PageTheme(
+    pageFormat: format.applyMargin(
+        left: 2.0 * PdfPageFormat.cm,
+        top: 4.0 * PdfPageFormat.cm,
+        right: 2.0 * PdfPageFormat.cm,
+        bottom: 2.0 * PdfPageFormat.cm),
+    buildBackground: (Context context) {
+      return FullPage(
+        ignoreMargins: true,
+        child: CustomPaint(
+          size: PdfPoint(format.width, format.height),
+          painter: (PdfGraphics canvas, PdfPoint size) {
+            context.canvas
+              ..setColor(lightGreen)
+              ..moveTo(0, size.y)
+              ..lineTo(0, size.y - 230)
+              ..lineTo(60, size.y)
+              ..fillPath()
+              ..setColor(green)
+              ..moveTo(0, size.y)
+              ..lineTo(0, size.y - 100)
+              ..lineTo(100, size.y)
+              ..fillPath()
+              ..setColor(lightGreen)
+              ..moveTo(30, size.y)
+              ..lineTo(110, size.y - 50)
+              ..lineTo(150, size.y)
+              ..fillPath()
+              ..moveTo(size.x, 0)
+              ..lineTo(size.x, 230)
+              ..lineTo(size.x - 60, 0)
+              ..fillPath()
+              ..setColor(green)
+              ..moveTo(size.x, 0)
+              ..lineTo(size.x, 100)
+              ..lineTo(size.x - 100, 0)
+              ..fillPath()
+              ..setColor(lightGreen)
+              ..moveTo(size.x - 30, 0)
+              ..lineTo(size.x - 110, 50)
+              ..lineTo(size.x - 150, 0)
+              ..fillPath();
+          },
+        ),
+      );
+    },
+  );
 }
 
 class Block extends StatelessWidget {