nativescript-demo/App_Resources/Android/src/main/res/values-v29/styles.xml

<?xml version="1.0" encoding="utf-8"?>
<resources xmlns:android="http://schemas.android.com/apk/res/android">

    <!-- Application theme -->
    <style name="AppThemeBase29" parent="AppThemeBase21">
        <item name="android:forceDarkAllowed">true</item>
    </style>

    <style name="AppTheme" parent="AppThemeBase29">
    </style>

</resources>