activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout
		xmlns:android="http://schemas.android.com/apk/res/android"
		xmlns:tools="http://schemas.android.com/tools"
		xmlns:app="http://schemas.android.com/apk/res-auto"
		android:layout_width="match_parent"
		android:layout_height="match_parent"
		tools:context=".MainActivity">

	<com.google.android.material.bottomappbar.BottomAppBar
			android:id="@+id/app_bar"
			android:layout_width="match_parent"
			android:layout_height="?attr/actionBarSize"
			app:backgroundTint="@color/colorPrimary"
			android:layout_gravity="bottom"/>

	<com.google.android.material.floatingactionbutton.FloatingActionButton
			android:src="@drawable/ic_add"
			android:id="@+id/fab"
			android:layout_width="wrap_content"
			android:layout_height="wrap_content"
			app:layout_anchor="@id/app_bar"
			app:backgroundTint="@color/colorPrimaryDark"/>

</androidx.coordinatorlayout.widget.CoordinatorLayout>