This so far has been working for me to have DroneCI behind an NGiNX reverse proxy working with Gitea

NGiNX Code⌗

nano /etc/nginx/sites-available/droneci.domain.com

ln -s /etc/nginx/sites-available/droneci.domain.com /etc/nginx/sites-enabled

upstream droneci {
        server 127.0.0.1:8080;
}
server {
        server_name droneci.domain.com drone.domain.com;

        listen 443 ssl http2;
        ssl_certificate            /etc/certs/droneci.domain.com/fullchain.crt;
        ssl_certificate_key        /etc/certs/droneci.domain.com/key;
        ssl_session_cache  builtin:1000  shared:SSL:10m;
        ssl_protocols TLSv1.2 TLSv1.3;

        location / {
                proxy_set_header X-Forwarded-For $remote_addr;
                proxy_set_header X-Forwarded-Proto $scheme;
                proxy_set_header Host droneci.domain.com;
                proxy_pass http://droneci;
                proxy_redirect off;
                proxy_http_version 1.1;
                proxy_buffering off;
                chunked_transfer_encoding off;
        }
}

Here is the code for the docker container⌗ 

docker run \
--volume=/var/lib/drone:/data \
--env=DRONE_GITEA_SERVER="https://git.domain.com" \
--env=DRONE_GITEA_CLIENT_ID="CLIENTIDHERE" \
--env=DRONE_GITEA_CLIENT_SECRET="CLIENTSECRETHERE" \
--env=DRONE_RPC_SECRET=RPCSECRETHERE \
--env=DRONE_SERVER_HOST="droneci.domain.com" \
--env=DRONE_SERVER_PROTO="https" \
--publish=8080:80 \
--restart=always \
--detach=true \
--name="droneci.domain.com" \
drone/drone:1