Du solltest auf dem Server des Hosters ja ein Verzeichnis ("Homeverzeichnis") haben, in dem auch (in einem Unterverzeichnis, z.B. namens www oder public_html) die Elgg-Installation abliegt. Nun solltest Du für das Datenverzeichnis in diesem Homeverzeichnis parallel zu dem public_html (NICHT in diesem Verzeichnis) ein neues Verzeichnis anlegen (nenne es bespielsweise "DATEN"), das von Elgg als das Datenverzeichnis verwendet werden kann. Wichtig ist, dass der Webserver in dieses Verzeichnis schreiben kann. Daher mußt Du eventuell die Zugriffsrechte des Verzeichnisses anpassen.

Bei der Installation von Elgg mußt Du dann den vollständigen Pfad zu dem Datenverzeichnis auf dem Server angeben (nicht den relativen Pfad von Deinem Homeverzeichnis). Wie genau der vollständige, absolute Pfad lautet, hängt aber von der Konfiguration des Servers ab und daher müßtest Du das den Support von all-Inkl fragen. Der Pfad könnte etwa "/home/ACCOUNTNAME/DATEN" lauten, aber es kann auf deinem Server auch anders sein.

Is there a way that I can change the background photo?

1 - Change this file

\mod\elgg_theme\views\default\graphics\cover.jpg

On your custom file with same name and extension.

2 - Run 'Upgrade' via Administration to clean the caches.

FYI: You can ask questions on the plugin page instead of creating a new discussion :)

Thank you Nikolai!

Much appreciated.

Dear Nikolai,

Many thanks for your message and the links you provided.

This was really helpful and after several attempts, I finally succeed with the extend method.

I have another question :

How can I replace the text logo by an image logo ?

Thanks again.

Have a nice day.

Thierry 

The links below are for previous Elgg versions but should work for the current release as well:

https://elgg.org/discussion/view/2804746/logo-in-default-theme-in-all-stable-elgg-version

https://elgg.org/discussion/view/2849336/how-to-change-the-logo-from-text-to-image

I forgot to mention that the easiest way to extend engine/theme.php is to use a hook in elgg_plugin.php instead of class:

'theme' => [
     'body-background-color' => '#000',
     'anchor-color' => '#000000',
],

The current version of Elgg doesn't need themes. These are individual cases for each developer.
Modern Elgg is an API build for creating custom applications.

And yes, Elgg and community are still active, - just look at our Telegram channel to be sure

Read this reply also.

The current version of Elgg doesn't need themes.

I wouldn't say that. The point is: themeing is highly individual. And the themes developed for Elgg 2.x or older won't work anymore on Elgg 3.x or newer. Main reason for that is that it got somewhat easier to customize some aspect of the look of Elgg sites. But this came with a loss of backward compatibility of themes.

In the end, theme plugins are not much different from other Elgg plugins. Maybe even easier to some extent because they would rather change only existing aspects of Elggs, i.e. the look, and not add functionality. It's mainly a matter of "overriding" already existing views of Elgg where you would modify for example CSS stuff in the views of your "theme plugin". One point that made customization easier on Elgg 3.x and 4.x is that CSS variables were introduced that you could alter via a plugin hook (so it got a little bit like coding in this point but you can change for example the color scheme easier this way in one place instead of having to alter possible several CSS files). See https://learn.elgg.org/en/stable/guides/themes.html for a introduction to theming. It would require some basic knowledge about how to create a simple Elgg plugin but you would be able to create you very own individual theme without the need to hire a developer to write a singular theme just for you (which might not be that cheap compared to other kind of plugins the developer might be able to divide the costs between several customers who have similar requirements).