Change path to mq

Help!
1

I am new to Haproxy and I am trying to do a simple change from <server_ip>/mq to <server_ip>:8161/admin

if I am trying to access ActiveMQ directly that works well:

<server_ip>:8161/admin

but with the Haproxy, sometimes I got 503 and if that works, it’s not load the resource at all (no css, no images…)
I don’t want to do redirect, just access it from /mq

frontend http
        bind *:80
        timeout client 60s
        mode http
        acl app path_end -i /mq
        use_backend appServer if app
        default_backend all

backend appServer
        timeout connect 10s
        timeout server 10s
        mode http
        http-request set-path /admin/
        server servermq <server_ip>:8161

backend all
        timeout connect 10s
        timeout server 10s
        mode http
        http-request set-path /admin/
        server servermq <server_ip>:8161

In the dev tools I can see errors like this:

Refused to apply style from 'http://<server_ip>/admin/styles/site.css' because its MIME type ('text/html') is not a supported stylesheet MIME type, and strict MIME checking is enabled.

there is issue load the resource on the fronted, but I am not sure how to fix this,
if you have any suggestions Thank you!