launcher/app/src/main/res/layout/activity_manage_widget_panels.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:fitsSystemWindows="true"
    tools:context=".ui.widgets.manage.ManageWidgetPanelsActivity">

    <com.google.android.material.appbar.AppBarLayout
        android:id="@+id/manage_widget_panels_appbar"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:background="@null"
        app:elevation="0dp"
        app:layout_constraintTop_toTopOf="parent">

        <androidx.constraintlayout.widget.ConstraintLayout
            android:layout_width="match_parent"
            android:layout_height="match_parent">

            <TextView
                android:id="@+id/manage_widget_panels_heading"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:gravity="center"
                android:minHeight="?actionBarSize"
                android:padding="@dimen/appbar_padding"
                android:text="@string/widget_panels_title"
                android:textAppearance="@style/TextAppearance.Widget.AppCompat.Toolbar.Title"
                android:textSize="30sp"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintStart_toStartOf="parent"
                app:layout_constraintTop_toTopOf="parent" />

            <ImageView
                android:id="@+id/manage_widget_panels_close"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:layout_marginEnd="8dp"
                android:contentDescription="@string/close"
                android:gravity="center"
                android:includeFontPadding="true"
                android:paddingLeft="16sp"
                android:paddingRight="16sp"
                android:src="@drawable/baseline_close_24"
                app:layout_constraintBottom_toBottomOf="parent"
                app:layout_constraintEnd_toEndOf="parent"
                app:layout_constraintTop_toTopOf="parent" />
        </androidx.constraintlayout.widget.ConstraintLayout>

    </com.google.android.material.appbar.AppBarLayout>

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/manage_widget_panels_recycler"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintTop_toBottomOf="@id/manage_widget_panels_appbar" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/manage_widget_panels_add_panel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"
        android:contentDescription="@string/add_widget_panel"
        android:src="@drawable/baseline_add_24"
        app:layout_anchor="@+id/manage_widget_panels_recycler"
        app:layout_anchorGravity="end|bottom"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>