Write these below codes in styles.xml
<style name="MyTabLayout" parent="Base.Widget.Design.TabLayout">
<item name="tabTextAppearance">@style/MyTabTextAppearance</item>
</style>
<style name="MyTabTextAppearance" parent="TextAppearance.AppCompat.Button">
<item name="android:textSize">18sp</item>
<item name="android:textColor">@android:color/white</item>
<item name="textAllCaps">true</item>
</style>
And in your tablayout, set the style like below.
<android.support.design.widget.TabLayout
style="@style/MyTabLayout"
android:layout_width="width"
android:layout_height="height"/>