ActionBar не показывается в эмуляторе

ActionBar не показывается в эмуляторе, но отображается во время редактирования Activity из программы. Какой момент в коде я упустил?

Код MainActivity.java

public class MainActivity extends Activity implements View.OnClickListener {
 private TextView mainText;
 private Button btnOk;
 private Button btnCancel;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);

    mainText = (TextView) findViewById(R.id.tvOut);
    btnOk = (Button) findViewById(R.id.btnOk);
    btnCancel = (Button) findViewById(R.id.btnCancel);

    btnOk.setOnClickListener(this);
    btnCancel.setOnClickListener(this);
}

@Override
public void onClick(View v) {
    switch (v.getId()) {
        case R.id.btnOk:
            mainText.setText("Ok");
            Log.v("myl", "Ok");
            Toast.makeText(this, "Ok", Toast.LENGTH_SHORT).show();
            break;
        case R.id.btnCancel:
            mainText.setText("Cancel");
            Log.v("myl", "Cancel");
            Toast.makeText(this, "Cancel", Toast.LENGTH_SHORT).show();
            break;
    }
}

}

Xml-код Activity

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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:background="@color/teal_200"
android:orientation="vertical">

<LinearLayout
    android:id="@+id/linearLayout1"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="30dp"
    android:background="@color/teal_700"
    android:orientation="vertical"
    tools:layout_editor_absoluteX="30dp"
    tools:layout_editor_absoluteY="30dp">

    <TextView
        android:id="@+id/tvOut"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:layout_marginBottom="50dp"
        android:text="TextView"></TextView>

    <Button
        android:id="@+id/btnOk"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text="OK"></Button>

    <Button
        android:id="@+id/btnCancel"
        android:layout_width="100dp"
        android:layout_height="wrap_content"
        android:layout_gravity="center_horizontal"
        android:text="Cancel"></Button>
</LinearLayout>
</androidx.constraintlayout.widget.ConstraintLayout>

Манифест-код

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.nikitafront.onclickbutton">
<application
    android:allowBackup="true"
    android:icon="@mipmap/ic_launcher"
    android:label="@string/app_name"
    android:roundIcon="@mipmap/ic_launcher_round"
    android:supportsRtl="true"
    android:theme="@style/Theme.AppCompat.DayNight.DarkActionBar">
    <activity android:name=".MainActivity">
        <intent-filter>
            <action android:name="android.intent.action.MAIN" />

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