ActionBar style as theme is ignored

Question

I'm having the following setup:

toolbar.xml

<android.support.v7.widget.Toolbar
        xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:tools="http://schemas.android.com/tools"
        xmlns:app="http://schemas.android.com/apk/res/com.citylifta"
        android:id="@+id/toolbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:theme="@style/ActionBarTheme" />

themes.xml:

<style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
    <item name="windowActionBar">false</item>
    <item name="actionBarTheme">@style/ActionBarTheme</item>
</style>

<style name="ActionBarTheme" parent="ThemeOverlay.AppCompat.Dark.ActionBar">
    <item name="android:textAllCaps">true</item>
    <item name="android:background">@color/dark_button</item>
</style>

now, if I omit the attr app:theme="@style/ActionBarTheme", the toolbar gets totally black...

How to define the toolbar's styling as a part of the AppTheme properly?