selector_tab_second.xml

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">

    <!-- radius should be half of the desired TabLayout height -->
    <corners
        android:radius="15dp"/>

    <!-- color of the selected tab -->
    <solid
        android:color="@color/colorBgTabSelected"/>

</shape>