add item background for popup menu items

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

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

@@ -81,6 +81,7 @@
     <style name="appActionBarPopupMenu" parent="@style/Widget.AppCompat.PopupMenu.Overflow">
         <item name="android:colorPrimary">@color/fg_inverse</item>
         <item name="android:textColorSecondary">@color/fontAppbar</item>
+        <item name="android:itemBackground">@color/appbar</item>
         <item name="android:background">@color/appbar</item>
         <item name="android:textColor">@color/high_emphasis_text</item>
         <item name="iconTint">@color/fontAppbar</item>