activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/black"
    android:orientation="vertical"
    tools:context=".MainActivity">


    <Button
        android:id="@+id/button"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_margin="30dp"
        android:layout_gravity="center"
        android:text="Button" />

    <Button
        android:id="@+id/button2"
        android:layout_width="200dp"
        android:layout_height="200dp"
        android:layout_marginStart="50dp"
        android:gravity="start|center_vertical"
        android:backgroundTint="#2196F3"
        android:textColor="@color/black"
        android:text="Button" />

    <Button
        android:id="@+id/button3"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="50dp"
        android:text="Button" />
</LinearLayout>