VoiceSearchButtonをタップしたときのエフェクトが四角い

###前提・実現したいこと
SearchViewに音声認識機能を追加し、
ToolbarにVoiceSearchButtonを追加したところ、
VoiceSearchButtonを長押ししたときのエフェクトが四角いです。
左側のxボタンと同じように丸くするにはどうしたらいいでしょうか。

###発生している問題・エラーメッセージ
マイクボタンを長押ししたときのエフェクトが四角い
左隣のxボタンは丸い

###該当のソースコード
activity_main.xml

activity_main.xml
1<?xml version="1.0" encoding="utf-8"?>
2<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
3    xmlns:app="http://schemas.android.com/apk/res-auto"
4    android:layout_width="match_parent"
5    android:layout_height="match_parent">
6    <LinearLayout
7        android:orientation="vertical"
8        android:layout_width="match_parent"
9        android:layout_height="match_parent">
10        <android.support.v7.widget.Toolbar
11            android:id="@+id/toolbar"
12            android:background="?attr/colorPrimary"
13            android:layout_width="match_parent"
14            android:layout_height="wrap_content"
15            app:theme="@style/ThemeOverlay.AppCompat.Dark" />
16        <TextView
17            android:id="@+id/result"
18            android:textSize="20sp"
19            android:layout_margin="10dp"
20            android:textColor="#FF34"
21            android:layout_width="match_parent"
22            android:layout_height="match_parent" />
23    </LinearLayout>
24</RelativeLayout>

styles.xml

styles.xml
1<resources>
2
3    <!-- Base application theme. -->
4    <style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
5        <!-- Customize your theme here. -->
6        <item name="colorPrimary">@color/colorPrimary</item>
7        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
8        <item name="colorAccent">@color/colorAccent</item>
9    </style>
10
11</resources>

AndroidManifest.xml

AndroidManifest.xml
1<?xml version="1.0" encoding="utf-8"?>
2<manifest xmlns:android="http://schemas.android.com/apk/res/android"
3    package="jp.co.araiyusuke.myapplication">
4
5    <application
6        android:allowBackup="true"
7        android:icon="@mipmap/ic_launcher"
8        android:label="@string/app_name"
9        android:supportsRtl="true"
10        android:theme="@style/AppTheme">
11        <activity
12            android:name=".MainActivity"
13            android:launchMode="singleTop"
14            >
15
16            <intent-filter>
17                <action android:name="android.intent.action.MAIN" />
18                <category android:name="android.intent.category.LAUNCHER" />
19            </intent-filter>
20
21            <intent-filter>
22                <action android:name="android.intent.action.SEARCH" />
23            </intent-filter>
24
25            <meta-data
26                android:name="android.app.default_searchable"
27                android:value=".MainActivity" />
28
29            <meta-data
30                android:name="android.app.searchable"
31                android:resource="@xml/searchable" />
32        </activity>
33    </application>
34</manifest>

res/xml/searchable.xml

res/xml/searchable.xml
1<?xml version="1.0" encoding="utf-8"?>
2<searchable
3    xmlns:android="http://schemas.android.com/apk/res/android"
4    android:label="@string/app_name"
5    android:hint="@string/hint"
6    android:voiceSearchMode="showVoiceSearchButton|launchRecognizer" />

res/menu/menu_search.xml

res/menu/menu_search.xml
1<?xml version="1.0" encoding="utf-8"?>
2<menu xmlns:android="http://schemas.android.com/apk/res/android"
3    xmlns:app="http://schemas.android.com/apk/res-auto">
4    <item
5        android:id="@+id/search_view"
6        android:title="@string/app_name"
7        app:actionViewClass="android.support.v7.widget.SearchView"
8        app:showAsAction="always" />
9</menu>

strings.xml

strings.xml
1<resources>
2    <string name="app_name">My Application</string>
3    <string name="hint">住所</string>
4</resources>

MainActivity.java

MainActivity.java
1import android.app.SearchManager;
2import android.content.Context;
3import android.content.Intent;
4import android.os.Bundle;
5import android.support.v7.app.AppCompatActivity;
6import android.support.v7.widget.SearchView;
7import android.support.v7.widget.Toolbar;
8import android.util.Log;
9import android.view.Menu;
10import android.view.MenuInflater;
11import android.widget.TextView;
12
13public class MainActivity extends AppCompatActivity {
14
15    private SearchView mSearchView;
16    @Override
17    protected void onCreate(Bundle savedInstanceState) {
18        super.onCreate(savedInstanceState);
19        setContentView(R.layout.activity_main);
20        setToolbar();
21    }
22
23    private void setToolbar() {
24        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
25        setSupportActionBar(toolbar);
26    }
27
28    @Override
29    public boolean onCreateOptionsMenu(Menu menu) {
30        MenuInflater inflater = getMenuInflater();
31        inflater.inflate(R.menu.menu_search, menu);
32        mSearchView = (SearchView) menu.findItem(R.id.search_view).getActionView();
33        mSearchView.setSubmitButtonEnabled(false);
34
35        mSearchView.setMaxWidth(Integer.MAX_VALUE);
36        SearchManager searchManager = (SearchManager) getSystemService(Context.SEARCH_SERVICE);
37        mSearchView.setSearchableInfo(searchManager.getSearchableInfo(getComponentName()));
38        mSearchView.findViewById(android.support.v7.appcompat.R.id.search_plate)
39                .setBackgroundColor(getResources().getColor(android.R.color.transparent));
40        mSearchView.findViewById(android.support.v7.appcompat.R.id.submit_area)
41                .setBackgroundColor(getResources().getColor(android.R.color.transparent));
42
43
44        mSearchView.setOnQueryTextListener(new android.support.v7.widget.SearchView.OnQueryTextListener() {
45            @Override
46            public boolean onQueryTextSubmit(String query) {
47                Log.d("onQueryTextSubmit", query);
48                return false;
49            }
50
51            @Override
52            public boolean onQueryTextChange(String query) {
53                Log.d("onQueryTextChange", query);
54                return false;
55            }
56        });
57
58        boolean autofocus = false;
59        mSearchView.setIconified(!autofocus);
60        mSearchView.setIconifiedByDefault(true);
61        return true;
62    }
63    @Override
64    protected void onNewIntent(Intent intent) {
65        setIntent(intent);
66        if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
67            String query = intent.getStringExtra(SearchManager.QUERY);
68            Log.d("onNewIntent", query);
69            boolean submit = false;
70            mSearchView.setQuery(query, submit);
71            TextView mResultTv  = (TextView) findViewById(R.id.result);
72            mResultTv.setText(query);
73        }
74    }
75}