Hello everybody,
I would like to change the backcolor question. I don't find the css file. Has anyone an idea ? thanks
It depends upon your theme, and possibly your version of Moodle, too. Let us know.
Also, "background" exists in many places. You will need to be more specific with your question.
In general, go to Site Admin, Appearance, pick your theme, and look for background color.
You need to look at how to theme Moodle. https://docs.moodle.org/dev/Themes