使用透明背景颜色和高程值0的组合。

showDialog(
                  context: context,
                  builder: (_) => Dialog(
                        backgroundColor: Colors.transparent,
                        elevation: 0.0,
                        child: IconButton(
                            icon: Image.asset('lib/images/last.png'),
                            iconSize: 260,
                        ),
                      ));

我想是关于海拔的？试着把它设为0

对话框带有黑色阴影的原因可能是小工具的高度或对话框的屏障颜色。

完整代码

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(title: const Text('Dialog Sample')),
        body: const Center(
          child: DialogExample(),
        ),
      ),
    );
  }
}

class DialogExample extends StatelessWidget {
  const DialogExample({super.key});

  @override
  Widget build(BuildContext context) {
    return TextButton(
      onPressed: () => showDialog<String>(
        barrierColor:Colors.transparent, #Color of the space around the dialog
        context: context,
        builder: (BuildContext context) => Dialog(
          backgroundColor :Colors.transparent, #Color of the dialog
          elevation:0, #elevation of the dialog
          child:Container(height:200,width:200,color:Colors.grey)
        ),
      ),
      child: const Text('Show Dialog'),
    );
  }
}

输出

希望这对你有帮助。快乐编码：）