styles.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <!-- Application theme -->
    <style name="AppTheme" parent="AppThemeBase">
        <item name="android:datePickerStyle">@style/SpinnerDatePicker</item>
        <item name="android:timePickerStyle">@style/SpinnerTimePicker</item>
    </style>

    <!-- Default style for DatePicker - in spinner mode -->
    <style name="SpinnerDatePicker" parent="android:Widget.Material.Light.DatePicker">
        <item name="android:datePickerMode">spinner</item>
    </style>

    <!-- Default style for TimePicker - in spinner mode -->
    <style name="SpinnerTimePicker" parent="android:Widget.Material.Light.TimePicker">
        <item name="android:timePickerMode">spinner</item>
    </style>

    <style name="NativeScriptToolbarStyle" parent="NativeScriptToolbarStyleBase">
        <item name="android:elevation">4dp</item>
    </style>    
</resources>