sample/src/main/res/drawable/control_bar_item_view_background_activated.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android" android:shape="rectangle">
    <corners android:radius="2dp" />
    <solid android:color="@color/item_selected_teal" />
</shape>