main_in.xml

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/main_rcv"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="45dp"
        android:layout_alignParentBottom="true"
        android:background="#aa000000"
        android:gravity="center">

        <ImageButton
            android:id="@+id/main_open_iv"
            android:background="@null"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="15dp"
            android:src="@drawable/open" />
    </RelativeLayout>
</merge