mkdocs: 404 page misses styles

[davidyuk]

Opening some not existing page like https://docs.aeternity.com/protocol/1ewefwefe I see

The reason is that it tries to load https://docs.aeternity.com/assets/stylesheets/main.0d440cfe.min.css (fails with 404) instead of https://docs.aeternity.com/protocol/assets/stylesheets/main.0d440cfe.min.css only on not found page