制作圆形自定义警报对话框：着色区域不正确

我已成功尝试使用以下代码制作自定义警报对话框。然而，当我试图使Constraint Layout在custom_dialog.xml有圆角，它表现出了故障：黑色（黑暗/有色）区不包括那些对圆角由于白色的区域。这就是我要说的：

我的代码MainActivity.kt：

package com.example.customdialog

import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.view.LayoutInflater
import android.view.View
import androidx.appcompat.app.AlertDialog
import kotlinx.android.synthetic.main.activity_main.*
import kotlinx.android.synthetic.main.custom_dialog.view.*

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
    }

    fun showDialog(view: View) {
        val mDialogView = LayoutInflater.from(this).inflate(R.layout.custom_dialog, null)
        val mBuilder = AlertDialog.Builder(this)
            .setView(mDialogView)

        val mAlertDialog = mBuilder.show()
        mDialogView.closeDialog.setOnClickListener {
            mAlertDialog.dismiss()
        }
    }
}

我的代码custom_dialog.xml：

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:background="@drawable/rounded_corners">

    <ImageView
        android:id="@+id/imageView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="141dp"
        android:layout_marginLeft="141dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="142dp"
        android:layout_marginRight="142dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        android:src="@mipmap/smiley_foreground"
        android:tint="#FFF"/>

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="WORKED!"
        android:textColor="#FFF"
        android:textSize="18sp"
        android:textStyle="bold"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/imageView" />

    <TextView
        android:id="@+id/textView3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:text="Apparently, the custom dialog worked"
        android:textColor="#FFF"
        android:textSize="18sp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView2" />

    <Button
        android:id="@+id/closeDialog"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="8dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:layout_marginBottom="16dp"
        android:background="@drawable/rounded_button"
        android:backgroundTint="#FFF"
        android:text="Close Dialog"
        android:textColor="@color/colorPrimary"
        android:textSize="18sp"
        android:textStyle="bold"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView3" />

</androidx.constraintlayout.widget.ConstraintLayout>

我的代码使Constraint Layoutfromcustom_dialog.xml四舍五入：

<?xml version="1.0" encoding="UTF-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <solid android:color="@color/colorPrimary"/>
    <corners android:radius="25dp"/>
    <padding android:left="0dp" android:top="0dp" android:right="0dp" android:bottom="0dp" />
</shape>

如何删除对话框周围的白色区域？