How to get rid of the default background of the Android DatePickerDialog in Android 4.4.4?

I have a Xamarin.Android project targeting API 25 and having API 19 as the minimum SDK, in one of the activities when a button is touched the following DatePickerDialog appears:

As you can see, I defined a custom drawable with rounded corner and used it in the DatePickerDialog. The issue is that I can't get rid of the default background that has a shadowed border when running my application on an Android 4.4.4 device(API 19).

On Android N device (API 25) everything seem to work properly, here is a screenshot:

I would like to know how to remove the default background in Android 4.4.4 devices, is there any useful xml style attribute? Or maybe a programmatic solution? I can't find any resource discussing this issue.

Details

DatePickerFragment implementation that I am using:

public class DatePickerFragment : Android.Support.V4.App.DialogFragment, 
    Android.App.DatePickerDialog.IOnDateSetListener
{
    public static readonly string TAG = "X:" + typeof(DatePickerFragment).Name.ToUpper();

    Action<DateTime> _dateSelectedHandler = delegate { };

    public static DatePickerFragment NewInstance(Action<DateTime> onDateSelected)
    {
        DatePickerFragment frag = new DatePickerFragment();
        frag._dateSelectedHandler = onDateSelected;

        return frag;
    }

    public override Dialog OnCreateDialog(Bundle savedInstanceState)
    {
        DateTime currently = DateTime.Now;
        DatePickerDialog dialog = new DatePickerDialog(Activity,
                                                       Resource.Style.MyDialogTheme,
                                                       this,
                                                       currently.Year,
                                                       currently.Month,
                                                       currently.Day);
        dialog.SetTitle("");
        return dialog;
    }

    public void OnDateSet(DatePicker view, int year, int monthOfYear, int dayOfMonth)
    {
        DateTime selectedDate = new DateTime(year, monthOfYear + 1, dayOfMonth);
        _dateSelectedHandler(selectedDate);
    }
}

Style applied to the DatePickerDialog

<style name="MyDialogTheme" parent="Theme.AppCompat.Light.Dialog">
    <item name="android:windowFrame">@null</item>
    <item name="android:windowIsFloating">true</item>
    <item name="android:windowContentOverlay">@null</item>
    <item name="android:windowBackground">@color/transparent</item>
    <item name="android:windowFrame">@color/transparent</item>
    <item name="android:colorBackgroundCacheHint">@null</item>
    <item name="android:background">@drawable/dialog_background</item>
    <item name="android:datePickerStyle">@style/MyDatePicker</item>
    <item name="android:backgroundDimEnabled">true</item>
</style>

dialog_background drawable

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" >
  <stroke android:width="3dp"
        android:color="@color/white" />

  <corners android:radius="10dp" />

  <solid android:color="@color/white" />
</shape>

MyDatePicker style definition

<style name="MyDatePicker" parent="android:Widget.Material.DatePicker">
    <item name="android:datePickerMode">spinner</item>
</style>