app/src/main/res/drawable/button_bg_round.xml
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item>
<shape android:shape="oval">
<stroke android:color="?attr/colorControlNormal" android:width="2dp" />
<solid android:color="@color/Transparent"/>
<size android:width="45dp" android:height="45dp"/>
</shape>
</item>
</selector>