Custom branding/logo

Since I have not yet found it in the forum, but I know the possibility from Kopano, I share my knowledge here.
You can realize an individual logo, CSS etc. as a plugin for grommunio-web.

You can set the configuration for all users in:
/etc/grommunio-web/config.php

// General grommunio Web theme. This will be loaded by default for every user
// (if the theme is installed as a plugin)
// Users can override the 'logged-in' theme in the settings.
//define("THEME", 'grommunioLighttheme');
define("THEME", 'meintheme');

Then create the folder:
/usr/share/grommunio-web/plugins/meintheme

With the content:
drwxr-xr-x 2 root root 4096 7. Jan 15:37 css
-rw-r--r-- 1 root root 1406 7. Nov 2020 favicon.ico
drwxr-xr-x 2 root root 4096 7. Nov 2020 img
-rw-r--r-- 1 root root 115 7. Jan 15:42 theme.json

theme.json
{
“display-name": ‘mytheme’,
“logo-large": ‘img/logo.png’,
“background-image": ‘img/background.png’,
“stylesheets“: [”css/meintheme1.css”, ‘css/meintheme2.css’]
}
css according to the examples in /usr/share/grommunio-web/client/themes/*/css/*. Or omit "styhesheets".