res/drawable/add_item_dialog_background.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle" >
    <solid android:color="@color/material_color_surface_container_highest" />
    <corners
        android:topLeftRadius="?android:attr/dialogCornerRadius"
        android:topRightRadius="?android:attr/dialogCornerRadius" />
</shape>