关于已继承兼容包的Activity怎么自定义标题栏，activity标题栏

package com.ocular.htcvive.uicustomview;

import android.app.Activity;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Window;

public class MainActivity extends Activity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_CUSTOM_TITLE);
        setContentView(R.layout.activity_main);
        getWindow().setFeatureInt(Window.FEATURE_CUSTOM_TITLE,R.layout.titlebar);
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="horizontal" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/back"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="上一步"/>

    <TextView
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="wrap_content"
        android:text="标题"
        android:textSize="18sp"
        android:gravity="center"/>

    <Button
        android:id="@+id/back1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="下一步"
        android:textSize="18sp"/>

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <style name="mystyle" parent="android:Theme.Light">
        <item name="android:windowTitleSize">45dp</item>
    </style>
</resources>

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.ocular.htcvive.uicustomview">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/mystyle">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>