<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>

    <style name="CalcButtonMedium" parent="android:style/Widget.Material.Button.Borderless">
        <item name="android:textSize">18sp</item>
        <item name="android:textColor">#FAFAFA</item>
    </style>

    <style name="CalcButtonLarge" parent="android:style/Widget.Material.Button.Borderless">
        <item name="android:textSize">28sp</item>
        <item name="android:textColor">#FAFAFA</item>
    </style>

</resources>

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>

    <style name="CalcButtonMedium" parent="@style/Widget.AppCompat.Button.Borderless">
        <item name="android:textSize">18sp</item>
        <item name="android:textColor">#FAFAFA</item>
    </style>

    <style name="CalcButtonLarge" parent="@style/Widget.AppCompat.Button.Borderless">
        <item name="android:textSize">28sp</item>
        <item name="android:textColor">#FAFAFA</item>
    </style>

</resources>

Fix strange color button before Lolipop
Fix strange color button before Lolipop
