Custom CSS for a self-hosted KoboToolbox Server

I installed kobotoolbox on my own server and was able to modify the logo and background image using the configuration offered by the administration space (jango).
I’m now looking to modify :

It should still be visible that this is a system not only/mainly developed by you, but based on an open source project.

Here an example from Kobo, using Enketo.

Hello wroos,
I can understand what you’re talking about. However, kobotoolbox is opensource and so we can adapt it to our needs.