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

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    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" />

    <FrameLayout
        android:id="@+id/mainFragmentContainer"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="?actionBarSize"
        android:layout_marginBottom="@dimen/bottom_navigation_height" />

    <com.aurelhubert.ahbottomnavigation.AHBottomNavigation
        android:id="@+id/mainBottomNav"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom" />
</androidx.coordinatorlayout.widget.CoordinatorLayout>