FossifyGallery/app/src/main/res/values/styles.xml

<resources>

    <style name="AppTheme" parent="AppTheme.Base">

    </style>

    <style name="FullScreenTheme.Base" parent="AppTheme">
        <item name="android:windowContentOverlay">@null</item>
        <item name="actionBarStyle">@style/MyFullScreenActionBar</item>
        <item name="android:actionBarStyle">@style/MyFullScreenActionBar</item>
    </style>

    <style name="FullScreenTheme" parent="FullScreenTheme.Base"/>

    <style name="MyFullScreenActionBar" parent="Widget.AppCompat.Light.ActionBar">
        <item name="titleTextStyle">@style/AppTheme.ActionBar.TitleTextStyle</item>
    </style>
</resources>