MEAN+Docker: Hide backend from outside the world - node.js

Question

I'm new to the backend. And I'm trying to server my application made on the MEAN stack using Docker-compose.
I have app: Docker + Nginx. Angular Frontend + Node.js Backend.
Problem: to hide my backend from outside the world
My docker-compose.yml: (one network)
version: '3'
services:
front: ..... # NO PORTS
back: .... # No PORTS
nginx:
.......
ports:
- "80:80"
- "443:443"
.......
certbot: .....
networks:
app-network:
driver: bridge
My nginx.conf
server {
listen 80;
server_name example.com www.example.com;
root /usr/share/nginx/html;
location / {
try_files $uri /index.html;
rewrite ^ https://$host$request_uri? permanent;
}
location ~ /.well-known/acme-challenge {
allow all;
root /var/www/html;
}
}
server {
listen 443 ssl http2;
listen [::]:443 ssl http2;
server_name ....
server_tokens off;
ssl_ ....
location /back {
try_files $uri #back;
}
location #back {
proxy_pass http://back:3001;
rewrite ^/back/(.*) /$1 break;
add_header X-Frame-Options "SAMEORIGIN" always;
add_header X-XSS-Protection "1; mode=block" always;
add_header X-Content-Type-Options "nosniff" always;
add_header Referrer-Policy "no-referrer-when-downgrade" always;
add_header Content-Security-Policy "default-src * data: 'unsafe-eval' 'unsafe-inline'" always;
}
location / {....}
location #front {
proxy_pass http://front:80;
add_header .....
}
}
Angular service TS:
getItems() {
return this.http.get('/back/items')
.pipe(map( res => res))
}