We can fix W3C validator errors from Wikimini.org:
https://validator.w3.org/nu/?doc=https%3A%2F%2Ffr.wikimini.org%2Fwiki%2FAccueil
The majority are related to the current skin in use.
Source code of the skin:
https://gitlab.wikimedia.org/repos/wikimedia-ch/wikimini.org-mediawiki-skin
Now we have: 144 messages.