sdk/platforms/android-27/data/res/layout/transient_notification.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
/* //device/apps/common/res/layout/transient_notification.xml
**
** Copyright 2006, 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.
*/
-->

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    android:background="?android:attr/toastFrameBackground">

    <TextView
        android:id="@android:id/message"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:layout_marginHorizontal="24dp"
        android:layout_marginVertical="15dp"
        android:layout_gravity="center_horizontal"
        android:textAppearance="@style/TextAppearance.Toast"
        android:textColor="@color/primary_text_default_material_light"
        />

</LinearLayout>