activity_demo.xml

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
              xmlns:tools="http://schemas.android.com/tools"
              android:layout_width="match_parent"
              android:layout_height="match_parent"
              android:fitsSystemWindows="false"
              android:orientation="vertical">

    <View
        android:id="@+id/view_state_bar"
        android:layout_width="match_parent"
        android:layout_height="@dimen/state_bar_height"
        android:background="@color/material_blue" />

    <FrameLayout
        android:layout_below="@+id/view_state_bar"
        android:id="@+id/container"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:ignore="MergeRootFrame" />

    <com.google.android.material.floatingactionbutton.FloatingActionButton
        android:id="@+id/fab"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:layout_margin="16dp"
        android:src="@drawable/ic_done"/>
</RelativeLayout>