notification_small.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_gravity="center"
    android:layout_height="match_parent">

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:gravity="center"
        android:text="TITLE"
        android:id="@+id/notification_title"
        style="@style/TextAppearance.Compat.Notification.Title" />

    <TextView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:gravity="center"
        android:text="TEXT"
        android:id="@+id/notification_text"
        style="@style/TextAppearance.Compat.Notification.Title" />

</LinearLayout>