Telegram / TMessagesProj / src / main / res / drawable / bg_voip_icon_btn.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
	<item android:state_checked="true">
		<shape android:shape="oval">
			<solid android:color="#3FFFFFFF"/>
		</shape>
	</item>
</selector>