sample/src/main/res/layout/tab_item.xml

<?xml version="1.0" encoding="utf-8"?>
<merge xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    tools:parentTag="android.widget.LinearLayout">

    <TextView
        android:id="@+id/titleView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="8dp"
        android:textColor="@color/text_color_dark"
        android:textSize="18sp"/>

    <View
        android:layout_width="match_parent"
        android:layout_height="2dp"
        android:background="@drawable/tab_bar_underline_selector"
        android:duplicateParentState="true"/>

</merge>