You can specify HTTP headers for a path/location in nginx in a static website and have it include arbitrary headers. Most standards respecting browsers (like Firefox) accept HTTP header specified CSS like,

    #/etc/nginx/sites-enabled/whatever.conf 
    location /this-isnt-for-you.html { 
        add_header Link "<//site.com/isntforyouheader.css>; REL=stylesheet";
    }

    $ curl -I http://site.com/this-isnt-for-you.html
    curl -I site.com
    HTTP/1.1 200 OK
    Server: nginx
    Date: Mon, 28 Nov 2022 18:08:01 GMT
    Content-Type: text/html
    Connection: keep-alive
    Link: <//site.com/isntforyouheader.css>; REL=stylesheet
    ...

This works to set CSS atributes only for a specific URL on my static websites using .html files. For nginx. But nginx is a very common and secure choice for static sites and available in everyone's repos. And you can probably add arbitrary headers per path with other static webservers configs too.