How can I configure base layers in Geonetwork 3.0.2?
I have tried to edit config-gui.xml and config-viewer.xml, but nothing happens.
Does it only work for the old version?
That's for the old UIs. Now you can configure it on the settings, editing the context as a string.
More information on the GeoNetwork documentation: http://geonetwork-opensource.org/manuals/trunk/eng/users/customizing-application/search-ui/configdefault.html