java/com/android/incallui/incall/impl/res/drawable/incall_button_background_unchecked.xml - platform/packages/apps/Dialer - Gitiles

 <?xml version="1.0" encoding="utf-8"?>
 <shape xmlns:android="http://schemas.android.com/apk/res/android"
   android:shape="oval">
   <solid android:color="@android:color/transparent"/>
 </shape>
	<?xml version="1.0" encoding="utf-8"?>
	<shape xmlns:android="http://schemas.android.com/apk/res/android"
	android:shape="oval">
	<solid android:color="@android:color/transparent"/>
	</shape>