Board Thread:Support Requests - Designing Your Wiki/@comment-44655805-20200506183843/@comment-9605025-20200506211124

That warning it erroneous. You are using the proper method. As I recently found out (see here), it is the result of what Fandom uses in the background to provide the syntax highlighting the verification. The program they use is not aware that you are not allowed to use the link tag. Link tags have to go in the HTML document's header; which you are not permitted to edit.

I assume you are using a UCP wiki? If you aren't sure what that is, see this announcement. The way CSS is currently loaded for UCP wikis is different from how it is loaded on legacy wikis. As a result,  does not work when used in Wikia.css. We have not yet confirmed this, but we suspect it may work from Common.css. If you are interested in the discussion about this, see here.