custom background state on toggle radio group button

layout.xml

<RadioGroup
        android:orientation="horizontal"
        android:id="@+id/radio_group"
        android:layout_width="match_parent"
        android:checkedButton="@+id/bt1"
        android:layout_height="wrap_content">

        <RadioButton
            android:id="@+id/bt1"
            android:background="@drawable/toggle_bg"
            android:layout_weight="1"
            android:text="Left"
            android:textColor="@color/colorPrimary"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <RadioButton
            android:id="@+id/bt2"
            android:background="@drawable/toggle_bg"
            android:layout_weight="1"
            android:textColor="@color/colorPrimary"
            android:text="right"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
</RadioGroup>

toggle_bg.xml

<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_checked="true"> <!-- selected -->
        <shape>
            <solid android:color="@android:color/white" />
            <stroke android:width="3px" android:color="@android:color/holo_blue_bright" />
            <corners android:radius="5dp" />
        </shape>
    </item>
    <item android:state_checked="false"> <!-- default -->
        <shape>
            <solid android:color="@android:color/black" />
            <stroke android:width="1px" android:color="@android:color/darker_gray" />
            <corners android:radius="5dp" />
        </shape>
    </item>
</selector>