DroidFS/app/src/main/res/layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:orientation="vertical"
    tools:context="sushi.hardcore.droidfs.MainActivity">

    <include android:id="@+id/toolbar" layout="@layout/toolbar"/>

    <ImageView
        android:id="@+id/image_logo"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_margin="30dp"
        android:src="@drawable/logo"
        app:tint="?attr/colorAccent"
        android:layout_weight="1"/>

    <androidx.constraintlayout.widget.ConstraintLayout
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1">

        <androidx.appcompat.widget.AppCompatButton
            android:id="@+id/button_open"
            android:layout_width="match_parent"
            android:layout_height="@dimen/main_activity_button_height"
            app:layout_constraintTop_toTopOf="parent"
            app:layout_constraintBottom_toTopOf="@id/button_create"
            android:layout_marginHorizontal="@dimen/main_activity_button_hor_margin"
            android:text="@string/open_volume"/>

        <androidx.appcompat.widget.AppCompatButton
            android:id="@+id/button_create"
            android:layout_width="match_parent"
            android:layout_height="@dimen/main_activity_button_height"
            app:layout_constraintTop_toBottomOf="@id/button_open"
            app:layout_constraintBottom_toTopOf="@id/button_change_password"
            android:layout_marginHorizontal="@dimen/main_activity_button_hor_margin"
            android:text="@string/create_volume"/>

        <androidx.appcompat.widget.AppCompatButton
            android:id="@+id/button_change_password"
            android:layout_width="match_parent"
            android:layout_height="@dimen/main_activity_button_height"
            app:layout_constraintTop_toBottomOf="@id/button_create"
            app:layout_constraintBottom_toBottomOf="parent"
            android:layout_marginHorizontal="@dimen/main_activity_button_hor_margin"
            android:text="@string/change_volume_password"/>

    </androidx.constraintlayout.widget.ConstraintLayout>

</LinearLayout>