nextcloud-talk-android/app/src/main/res/values/styles.xml

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.MaterialComponents.Light.NoActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorPrimary</item>
        <item name="android:panelFullBackground">@color/colorPrimary</item>
        <item name="android:itemBackground">@color/colorPrimary</item>
    </style>
</resources>