1.首先建立一个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:background="#1f1f1f"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="40dp"
        android:paddingLeft="30dp"
        android:paddingRight="30dp">
        <Button
            android:id="@+id/button_level_1"
            android:layout_width=