Cannot set text color in viewer popups / bookmarks list, outline, ...

Where can the color for the text in the viewer popups be set? I have attached a screenshot from the bookmarks popup, but it also applies to outline.
We are using the light theme and I tried to overwrite App_AlertDialogStyle in ViewLib/src/main/res/values/styles.xml:

<style name="App_AlertDialogStyle" parent="android:Theme.DeviceDefault.Light.Dialog.Alert">
<item name="android:textColor">@color/tab_text_color</item>
<item name="android:editTextColor">@color/tab_text_color</item>
<item name="android:color">@color/tab_text_color</item>
<item name="android:solidColor">@color/tab_text_color</item>
<item name="android:textColorPrimary">@color/tab_text_color</item>
<item name="android:textColorAlertDialogListItem">@color/tab_text_color</item>

@color/tab_text_color is #202020, so I do not understand why the color is so light. Could you please give me a hint where to set the color? Thanks