Avoid external CSS in the code. 404 error page.

[PeopleInside]

When not found 404 error page is showed, the CSS is not taken by the open source code but from https://cdn.uvdesk.com/uvdesk/css/main.css

https://github.com/uvdesk/community-skeleton/blob/94166612747f8a8d87d70b0e28e5c235f25afc4c/templates/errors/error.html.twig#L10

Please include this CSS in the open source project and avoid load of external CSS also because cannot be maybe fixed by the user if some issue occurs also is better to have self-hosted as the other code.