CSS and other resources fail to load when running the Docker image through an nginx proxy at subdomain

[dandv]

I'm running the Monica Docker image per the instructions on that page on a Digital Ocean VPS.

When I go to mydomain.com:8080, Monica runs fine. But I want to access Monica at a subdomain, monica.mydomain.com, so I'm using the following simple nginx config:

server {
  listen 443 ssl http2;
  listen [::]:443 ssl http2;

  server_name monica.mydomain.com;
  ssl_certificate     ...; # managed by Certbot
  ssl_certificate_key ...;   # managed by Certbot

  location / {
    proxy_pass http://localhost:8080/;
    add_header 'Access-Control-Allow-Origin' '$http_origin';
  }
}

The problem is that CSS/PNG/SVG requests are made to localhost:8080. I've tried running the image with the VIRTUAL_HOST and APP_URL variables set to monica.mydomain.com but that had no effect on the URLs generated for CSS resources.

sudo docker run -it --link "$mysqlCid":mysql -e DB_HOST=mysql -e APP_URL=https://monica.mydomain.com -p 8080:80 monica

I'm probably missing something simple.