How does 404.md work?

[Stwissel]

I added a 404.md to my site and ran into an issue (see below), so I tried to create a minimal reproducer, but there the 404.md was ignored and only the default rendered. So I wonder: what is needed (in mkdocs.yml I presume) to trigger a 404.md pickup?

The problem I ran into:
When the non-existing url contains a path, css and js aren't get picked up. So mysite.com/does-not-exist renders correctly. While mysite.com/this/does-not-exist fails.

Identified reason: the js/css path in the rendered 404 are relative, not absolute.

Help is very much appreciated

[squidfunk]

As far as I know, MkDocs doesn't support overriding the 404 page with an .md file – it must be a static template. This is not exclusive to Material for MkDocs, but to all MkDocs themes. Feel free to take this upstream.

[Stwissel]

That's interesting. The repo I worked with didn't have a 404.md and I created one out of [curiosity|ignorance|serendipity] (pick one). And it worked. As suggested, I'll take it upstream.

[Stwissel]

Happy to report: 404.md is a working feature of mkdocs, I was able to create a minimal reproducer (rendered here).
Problem occurs in vanilla mkdocs already. Reported upstream

Thx for the help!