added bend_box

lib/src/bend_box.dart

@@ -0,0 +1,40 @@
+import 'package:flutter/material.dart';
+
+class BendBox extends StatelessWidget {
+  final EdgeInsets inward;
+  final Color color;
+
+  BendBox({this.inward = const EdgeInsets.all(0), this.color = Colors.red});
+
+  Widget build(BuildContext context) {
+    return CustomPaint(painter: _BendBoxPainter(inward: inward, color: color));
+  }
+}
+
+class _BendBoxPainter extends CustomPainter {
+  final EdgeInsets inward;
+  final Color color;
+
+  _BendBoxPainter({this.inward, this.color});
+
+  void paint(Canvas canvas, Size size) {
+    final paint = Paint()
+      ..style = PaintingStyle.fill
+      ..isAntiAlias = true
+      ..color = color;
+
+    final path = Path()
+      ..moveTo(0, 0)
+      ..quadraticBezierTo(size.width / 2, inward.top, size.width, 0)
+      ..quadraticBezierTo(
+          size.width - inward.left, size.height / 2, size.width, size.height)
+      ..quadraticBezierTo(
+          size.width / 2, size.height - inward.bottom, 0, size.height)
+      ..quadraticBezierTo(inward.left, size.height / 2, 0, 0)
+      ..close();
+
+    canvas.drawPath(path, paint);
+  }
+
+  bool shouldRepaint(CustomPainter oldDelegate) => true;
+}