Center(
  child: GestureDetector(
    onTap: () {
      print("Button Clicked");
    },
    child: Container(
      width: 120.0,
      height: 120.0,
      decoration: BoxDecoration(
        color:  const Color.fromRGBO(60, 60, 60, 1.0),
        gradient: const LinearGradient(
          begin: Alignment.topLeft,
          end: Alignment.bottomRight,
          colors: <Color>[
            Color.fromRGBO(70, 70, 70, 1.0),
            Color.fromRGBO(70, 70, 70, 0.3),
          ]
        ),
        borderRadius: BorderRadius.circular(60),
        boxShadow: const [
          BoxShadow(
            color: Color.fromRGBO(30, 30, 30, 0.2),
            spreadRadius: 4,
            blurRadius: 8,
            offset: Offset(4, 4)
          ),
          BoxShadow(
            color: Color.fromRGBO(180, 180, 180, 0.1),
            spreadRadius: 2,
            blurRadius: 8,
            offset: Offset(-2, -2)
          ),
        ]
      ),
      child: Center(
        child: Container(
          width: 118,
          height: 118,
          decoration: BoxDecoration(
            color:  const Color.fromRGBO(60, 60, 60, 1.0),
            gradient: const LinearGradient(
              begin: Alignment.topLeft,
              end: Alignment.bottomRight,
              colors: <Color>[
                Color.fromRGBO(50, 50, 50, 1.0),
                Color.fromRGBO(70, 70, 70, 1.0),
              ]
            ),
            borderRadius: BorderRadius.circular(60),
            boxShadow: const [
              BoxShadow(
                color: Color.fromRGBO(30, 30, 30, 0.2),
                spreadRadius: 1,
                blurRadius: 4,
                offset: Offset(2, 2)
              ),
            ]
          ),
          child: Center(
            child: Container(
              width: 100,
              height: 100,
              decoration: BoxDecoration(
                color:  const Color.fromRGBO(60, 60, 60, 1.0),
                gradient: const LinearGradient(
                  begin: Alignment.topLeft,
                  end: Alignment.bottomRight,
                  colors: <Color>[
                    Color.fromRGBO(80, 80, 80, 1.0),
                    Color.fromRGBO(40, 40, 40, 1.0),
                  ]
                ),
                borderRadius: BorderRadius.circular(60),
                border: Border.all(
                  color: const Color.fromRGBO(0, 220, 240, 0.7),
                  width: 1,
                ),
                boxShadow: const [
                  BoxShadow(
                    color: Color.fromRGBO(30, 30, 30, 0.2),
                    spreadRadius: 1,
                    blurRadius: 4,
                    offset: Offset(2, 2)
                  ),
                ]
              ),
              child:  Center(
                child: Text(
                  "283",
                  style: GoogleFonts.getFont(
                    "Bubbler One",
                    textStyle: const TextStyle(
                      fontSize: 36,
                      fontWeight: FontWeight.w100,
                      color: Color.fromRGBO(190, 190, 190, 0.8),
                    ),
                  )
                ),
              ),
            )
          )
        )
      ),
    ),
  ),
),

const CustomPaint({
  Key? key,
  CustomPainter? painter,
  CustomPainter? foregroundPainter,
  Size size = Size.zero,
  bool isComplex = false,
  bool willChange = false,
  Widget? child
})

Center(
  child: CustomPaint(
    size: Size(300, 300),
    painter: _SimplePainter()
  ),
)

CustomPaint(
  painter: Sky(),
  child: const Center(
    child: Text(
      'Once upon a time...',
      style: TextStyle(
        fontSize: 40.0,
        fontWeight: FontWeight.w900,
        color: Color(0xFFFFFFFF),
      ),
    ),
  ),
)

class Sky extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final Rect rect = Offset.zero & size;
    const RadialGradient gradient = RadialGradient(
      center: Alignment(0.7, -0.6),
      radius: 0.2,
      colors: <Color>[Color(0xFFFFFF00), Color(0xFF0099FF)],
      stops: <double>[0.4, 1.0],
    );
    canvas.drawRect(
      rect,
      Paint()..shader = gradient.createShader(rect),
    );
  }

  @override
  SemanticsBuilderCallback get semanticsBuilder {
    return (Size size) {
    // 太陽の絵が描かれた四角形に「太陽」というラベルを付けて、注釈を付ける。
    // 端末で音声合成機能が有効になっている場合、ユーザーはこの絵の中の太陽の位置をタッチして確認することができます。太陽をタッチしてください。
      Rect rect = Offset.zero & size;
      final double width = size.shortestSide * 0.4;
      rect = const Alignment(0.8, -0.9).inscribe(Size(width, width), rect);
      return <CustomPainterSemantics>[
        CustomPainterSemantics(
          rect: rect,
          properties: const SemanticsProperties(
            label: 'Sun',
            textDirection: TextDirection.ltr,
          ),
        ),
      ];
    };
  }

  // このスカイペインターにはフィールドがないので、常に同じものを描き、セマンティクス情報も同じです。
  // そのため、ここでは false を返します。もしフィールドがあれば（コンストラクタで設定されている）、oldDelegateの同じフィールドと異なるものがあればtrueを返すことになります。
  @override
  bool shouldRepaint(Sky oldDelegate) => false;
  @override
  bool shouldRebuildSemantics(Sky oldDelegate) => false;
}

import 'package:flutter/material.dart';

class Sun extends StatelessWidget {

  const Sun({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Sky')
      ),
      body: Center(
        child: CustomPaint(
          painter: Sky(),
          child: const Center(
            child: Text(
              'Once upon a time...',
              style: TextStyle(
                fontSize: 40.0,
                fontWeight: FontWeight.w900,
                color: Color(0xFFFFFFFF),
              ),
            ),
          ),
        )
      )
    );
  }
}

class Sky extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    final Rect rect = Offset.zero & size;
    const RadialGradient gradient = RadialGradient(
      center: Alignment(0.7, -0.6),
      radius: 0.2,
      colors: <Color>[Color(0xFFFFFF00), Color(0xFF0099FF)],
      stops: <double>[0.4, 1.0],
    );
    canvas.drawRect(
      rect,
      Paint()..shader = gradient.createShader(rect),
    );
  }
  @override
  bool shouldRepaint(Sky oldDelegate) => false;
}

void paint(
  Canvas canvas,
  Size size
)

bool shouldRepaint(
  covariant CustomPainter oldDelegate
)