wulkanowy-mod/app/src/main/res/layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/mainContainer"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.material.appbar.MaterialToolbar
        android:id="@+id/mainToolbar"
        style="@style/Widget.MaterialComponents.Toolbar.Surface"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:contentInsetStartWithNavigation="0dp"
        app:layout_constraintTop_toTopOf="parent" />

    <androidx.fragment.app.FragmentContainerView
        android:id="@+id/mainFragmentContainer"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        app:layout_constraintBottom_toTopOf="@id/mainBottomNav"
        app:layout_constraintTop_toBottomOf="@id/mainToolbar" />

    <com.aurelhubert.ahbottomnavigation.AHBottomNavigation
        android:id="@+id/mainBottomNav"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toBottomOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>