Android Kotlin Usage Tutorial
Thanks to Renato Ferreiras observation.
If I use this code, the header text will cover the indicator. To correct it, use this for padding the list_header TextView:
android:paddingLeft="?android:attr/expandableListPreferredItemPaddingLeft"
and for the list_item:
android:paddingLeft="?android:attr/expandableListPreferredChildPaddingLeft"