<resources>

    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <item name="colorPrimary">@color/red</item>
        <item name="colorPrimaryDark">@color/dark_red</item>
        <item name="colorAccent">@color/gray</item>

        <item name="android:colorBackground">@color/soothing_blue</item>
        <item name="android:buttonStyle">@style/BeatBoxButton</item>
    </style>

    <style name="BeatBoxButton" parent="android:style/Widget.Holo.Button">
        <item name="android:background">@drawable/button_beat_box_normal</item>
    </style>

</resources>

<resources>

    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <item name="colorPrimary">@color/red</item>
        <item name="colorPrimaryDark">@color/dark_red</item>
        <item name="colorAccent">@color/gray</item>

        <item name="android:colorBackground">@color/soothing_blue</item>
        <item name="android:buttonStyle">@style/BeatBoxButton</item>
    </style>

    <style name="BeatBoxButton" parent="android:style/Widget.Holo.Button">
        <item name="android:background">@drawable/button_beat_box</item>
    </style>

</resources>

Use drawable selector from BeatBoxButton style
Use drawable selector from BeatBoxButton style
