godot/platform/android/java/editor/src/main/res/values/themes.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
	<style name="GodotEditorTheme" parent="@android:style/Theme.Black.NoTitleBar.Fullscreen">
	</style>

	<style name="GodotEditorSplashScreenTheme" parent="Theme.SplashScreen.IconBackground">
		<!-- Set the theme of the Activity that directly follows your splash
		screen. This is required. -->
		<item name="postSplashScreenTheme">@style/GodotEditorTheme</item>
	</style>
</resources>