packages/SystemUI/res/layout/biometric_dialog.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  ~ Copyright (C) 2018 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: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:scaleType="center" />

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:gravity="bottom"
        android:background="@color/biometric_dialog_dim_color"
        android:orientation="vertical">

        <!-- This is not a Space since Spaces cannot be clicked -->
        <View
            android:id="@+id/space"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1" />

        <ScrollView
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="horizontal">

                <!-- This is not a Space since Spaces cannot be clicked. The width of this changes
                depending on horizontal/portrait orientation -->
                <View
                    android:id="@+id/left_space"
                    android:layout_weight="1"
                    android:layout_width="0dp"
                    android:layout_height="match_parent"/>

                    <LinearLayout
                        android:id="@+id/dialog"
                        android:layout_width="match_parent"
                        android:layout_height="wrap_content"
                        android:orientation="vertical"
                        android:background="@drawable/biometric_dialog_bg"
                        android:layout_marginBottom="@dimen/biometric_dialog_border_padding"
                        android:layout_marginLeft="@dimen/biometric_dialog_border_padding"
                        android:layout_marginRight="@dimen/biometric_dialog_border_padding">

                        <TextView
                            android:id="@+id/title"
                            android:fontFamily="@*android:string/config_headlineFontFamilyMedium"
                            android:layout_width="match_parent"
                            android:layout_height="wrap_content"
                            android:layout_marginEnd="24dp"
                            android:layout_marginStart="24dp"
                            android:layout_marginTop="24dp"
                            android:gravity="@integer/biometric_dialog_text_gravity"
                            android:textSize="20sp"
                            android:textColor="?android:attr/textColorPrimary"/>

                        <TextView
                            android:id="@+id/subtitle"
                            android:layout_width="match_parent"
                            android:layout_height="wrap_content"
                            android:layout_marginTop="8dp"
                            android:layout_marginStart="24dp"
                            android:layout_marginEnd="24dp"
                            android:gravity="@integer/biometric_dialog_text_gravity"
                            android:textSize="16sp"
                            android:textColor="?android:attr/textColorPrimary"/>

                        <TextView
                            android:id="@+id/description"
                            android:layout_width="match_parent"
                            android:layout_height="wrap_content"
                            android:layout_marginEnd="24dp"
                            android:layout_marginStart="24dp"
                            android:gravity="@integer/biometric_dialog_text_gravity"
                            android:paddingTop="8dp"
                            android:textSize="16sp"
                            android:textColor="?android:attr/textColorPrimary"/>

                        <ImageView
                            android:id="@+id/biometric_icon"
                            android:layout_width="@dimen/biometric_dialog_biometric_icon_size"
                            android:layout_height="@dimen/biometric_dialog_biometric_icon_size"
                            android:layout_gravity="center_horizontal"
                            android:layout_marginTop="48dp"
                            android:scaleType="fitXY" />

                        <TextView
                            android:id="@+id/error"
                            android:layout_width="match_parent"
                            android:layout_height="wrap_content"
                            android:layout_marginEnd="24dp"
                            android:layout_marginStart="24dp"
                            android:paddingTop="16dp"
                            android:paddingBottom="24dp"
                            android:textSize="12sp"
                            android:gravity="center_horizontal"
                            android:accessibilityLiveRegion="polite"
                            android:textColor="?android:attr/textColorSecondary"/>

                        <LinearLayout
                            android:layout_width="match_parent"
                            android:layout_height="72dip"
                            android:paddingTop="24dp"
                            android:layout_gravity="center_vertical"
                            style="?android:attr/buttonBarStyle"
                            android:orientation="horizontal"
                            android:measureWithLargestChild="true">
                            <Space android:id="@+id/leftSpacer"
                                android:layout_width="12dp"
                                android:layout_height="match_parent"
                                android:visibility="visible" />
                            <!-- Negative Button -->
                            <Button android:id="@+id/button2"
                                android:layout_width="wrap_content"
                                android:layout_height="match_parent"
                                style="@*android:style/Widget.DeviceDefault.Button.Borderless.Colored"
                                android:gravity="center"
                                android:maxLines="2" />
                            <Space android:id="@+id/middleSpacer"
                                android:layout_width="0dp"
                                android:layout_height="match_parent"
                                android:layout_weight="1"
                                android:visibility="visible" />
                            <!-- Positive Button -->
                            <Button android:id="@+id/button1"
                                android:layout_width="wrap_content"
                                android:layout_height="match_parent"
                                style="@*android:style/Widget.DeviceDefault.Button.Colored"
                                android:gravity="center"
                                android:maxLines="2"
                                android:text="@string/biometric_dialog_confirm"
                                android:visibility="gone"/>
                            <!-- Try Again Button -->
                            <Button android:id="@+id/button_try_again"
                                android:layout_width="wrap_content"
                                android:layout_height="match_parent"
                                style="@*android:style/Widget.DeviceDefault.Button.Colored"
                                android:gravity="center"
                                android:maxLines="2"
                                android:text="@string/biometric_dialog_try_again"
                                android:visibility="gone"/>
                            <Space android:id="@+id/rightSpacer"
                                android:layout_width="12dip"
                                android:layout_height="match_parent"
                                android:visibility="visible" />
                        </LinearLayout>
                    </LinearLayout>

                <!-- This is not a Space since Spaces cannot be clicked. The width of this changes
                depending on horizontal/portrait orientation -->
                <View
                    android:id="@+id/right_space"
                    android:layout_weight="1"
                    android:layout_width="0dp"
                    android:layout_height="match_parent" />

            </LinearLayout>

        </ScrollView>

    </LinearLayout>

</FrameLayout>