res/layout/fragment_preview.xml

<!--
  ~ Copyright (C) 2021 The Android Open Source Project
  ~
  ~ Licensed under the Apache License, Version 2.0 (the "License");
  ~ you may not use this file except in compliance with the License.
  ~ You may obtain a copy of the License at
  ~
  ~      http://www.apache.org/licenses/LICENSE-2.0
  ~
  ~ Unless required by applicable law or agreed to in writing, software
  ~ distributed under the License is distributed on an "AS IS" BASIS,
  ~ WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ~ See the License for the specific language governing permissions and
  ~ limitations under the License.
  -->

<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
             android:background="@color/preview_background_color"
             android:layout_width="match_parent"
             android:layout_height="match_parent">

    <androidx.viewpager2.widget.ViewPager2
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/preview_viewPager"
        android:layout_gravity="center"/>

    <!-- Adds scrim for Toolbar -->
    <FrameLayout
        android:id="@+id/preview_top_scrim"
        android:layout_width="match_parent"
        android:layout_height="@dimen/preview_toolbar_scrim_height"
        android:background="@drawable/preview_gradient_desc"
        android:layout_gravity="top"
        android:visibility="gone"/>

    <!-- Adds scrim for deselect and Add button -->
    <FrameLayout
        android:id="@+id/preview_bottom_scrim"
        android:layout_width="match_parent"
        android:layout_height="@dimen/preview_deselect_scrim_height"
        android:background="@drawable/preview_gradient_asc"
        android:layout_gravity="bottom"
        android:visibility="gone"/>

    <FrameLayout
        android:id="@+id/preview_bottom_bar"
        android:layout_gravity="bottom"
        android:layout_width="match_parent"
        android:layout_height="@dimen/picker_bottom_bar_size"
        android:paddingHorizontal="@dimen/preview_buttons_padding_horizontal">

        <!-- Buttons for Preview on Long press. Visible by default -->
        <Button
            android:id="@+id/preview_add_or_select_button"
            android:layout_width="@dimen/preview_add_or_select_width"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:backgroundTint="@color/preview_highlight_color"
            android:paddingVertical="@dimen/picker_bottom_bar_buttons_vertical_gap"
            android:text="@string/add"
            android:textAllCaps="false"
            android:textColor="@color/preview_default_grey"
            style="@style/MaterialButtonStyle"/>

        <!-- Buttons for Preview on View Selected. Hidden by default -->
        <Button
            android:id="@+id/preview_select_check_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="start|center_vertical"
            android:paddingStart="@dimen/preview_deselect_padding_start"
            android:paddingVertical="@dimen/picker_bottom_bar_buttons_vertical_gap"
            android:background="@android:color/transparent"
            android:drawableLeft="@drawable/preview_check"
            android:drawableTint="@color/preview_highlight_color"
            android:textAllCaps="false"
            android:text="@string/deselect"
            android:textColor="@color/picker_default_white"
            android:visibility="gone"
            style="@style/MaterialBorderlessButtonStyle"/>

        <Button
            android:id="@+id/preview_add_button"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="end|center_vertical"
            android:backgroundTint="@color/preview_highlight_color"
            android:paddingVertical="@dimen/picker_bottom_bar_buttons_vertical_gap"
            android:text="@string/add"
            android:textAllCaps="false"
            android:textColor="@color/preview_default_grey"
            android:visibility="gone"
            style="@style/MaterialButtonStyle"/>
    </FrameLayout>
</FrameLayout>