nginx proxy pass ip from url

Question

I have multiple web servers with IP address say 172.18.1.1 to 172.18.1.20, hosting different website on 443(https) and A nginx server which I need to use for proxying above servers.

Example : My nginx server IP is https://10.220.5.39:9200 by giving web server in URL , I need to show the websites

i.e. https://10.220.5.39:9200/proxy/172.18.1.1, should get website of https://172.18.1.1

AND

https://10.220.5.39:9200/proxy/172.18.1.2, should get website of https://172.18.1.2

location /proxy/(?<uniqueId>[^/]+).* {
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_pass    https://$uniqueId/;
}

But it is not working , I can not use redirect , since client will not have access to web servers directly

Also some website use css file from route i.e. href="/static/theme.css"

because of which in browser console we are getting

not found https://10.220.5.39:9200/static/theme.css

Is this even possible with nginx