session-android/res/values-notnight-v21/styles.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>

    <style name="Widget.Session.Button.Common.ProminentOutline">
        <item name="android:background">@drawable/prominent_outline_button_medium_background</item>
        <item name="android:textColor">?android:textColorPrimary</item>
    </style>

    <style name="Widget.Session.Button.Common.ProminentFilled">
        <item name="android:background">@drawable/prominent_filled_button_medium_background</item>
        <item name="android:textColor">@android:color/white</item>
    </style>

</resources>