packages/SystemUI/res/layout/auth_container_view.xml

<!--
  ~ Copyright (C) 2019 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
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  ~ distributed under the License is distributed on an "AS IS" BASIS,
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  ~ See the License for the specific language governing permissions and
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<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/layout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <ImageView
        android:id="@+id/background"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="@color/biometric_dialog_dim_color"
        android:contentDescription="@string/biometric_dialog_empty_space_description"/>

    <View
        android:id="@+id/panel"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:background="?android:attr/colorBackgroundFloating"
        android:elevation="@dimen/biometric_dialog_elevation"/>

    <ScrollView
        android:id="@+id/biometric_scrollview"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal|bottom"
        android:layout_margin="@dimen/biometric_dialog_border_padding"
        android:elevation="@dimen/biometric_dialog_elevation"/>

</FrameLayout>