How to resolve nginx failure to restart after updating configuration files

I am having issues restarting nginx restart. I'm very new to ubuntu and nginix. I am trying to change the configuration of nginx.conf and default.conf(newly created). My main goal is to deploy my MERN app to Amazon Ec2

Here is my configuration respectively

server {
    #listen       80;
    listen 80 default_server;
    listen [::]:80 default_server;
    server_name  yourdomain.com;

    access_log /home/ubuntu/client/server_logs/host.access.log main;

    location / {
        root   /home/ubuntu/client/deploy;
        index  index.html index.htm;
        try_files $uri /index.html;
        add_header X-Frame-Options SAMEORIGIN;
        add_header X-Content-Type-Options nosniff;
        add_header X-XSS-Protection "1; mode=block";
        add_header Strict-Transport-Security "max-age=31536000; includeSubdomains;";
    }

    error_page   500 502 503 504  /50x.html;
    location = /50x.html {
        root   /usr/share/nginx/html;
    }

    server_tokens off;

    location ~ /\.ht {
        deny  all;
    }

}

user ubuntu;
worker_processes  1;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;

events {
    worker_connections  1024;
}

http {
    include       /etc/nginx/mime.types;
    default_type  application/octet-stream;

    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  /var/log/nginx/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    client_body_buffer_size 100k;
    client_header_buffer_size 1k;
    client_max_body_size 100k;
    large_client_header_buffers 2 1k;
    client_body_timeout 10;
    client_header_timeout 10;
    keepalive_timeout 5 5;
    send_timeout 10;
    server_tokens off;
    #gzip  on; on;

    include /etc/nginx/conf.d/*.conf;
}

if i try to restart nginx i with the following command "sudo service nginx restart" get the following error:

Job for nginx.service failed because the control process exited with an error code.
See "systemctl status nginx.service" and "journalctl -xe" for details.

I really need someone to tell me what am doing wrong because of my little experience with ubuntu and nginx. or is there any link i can access that will be helpful in understanding nginx configurations. Any help will be appreciated

out put from systemctl status nginx.service and journalctl -xe":

● nginx.service - A high performance web server and a reverse proxy server
     Loaded: loaded (/lib/systemd/system/nginx.service; enabled; vendor preset: enabled)
     Active: failed (Result: exit-code) since Sat 2020-11-21 12:23:42 UTC; 22s ago
       Docs: man:nginx(8)
    Process: 21094 ExecStartPre=/usr/sbin/nginx -t -q -g daemon on; master_process on; (code=exited, status=1/FAILURE)

Nov 21 12:23:42 ip-172-31-23-90 systemd[1]: Starting A high performance web server and a reverse proxy server...
Nov 21 12:23:42 ip-172-31-23-90 nginx[21094]: nginx: [emerg] unknown directive "sten" in /etc/nginx/conf.d/default.conf:1
Nov 21 12:23:42 ip-172-31-23-90 nginx[21094]: nginx: configuration file /etc/nginx/nginx.conf test failed
Nov 21 12:23:42 ip-172-31-23-90 systemd[1]: nginx.service: Control process exited, code=exited, status=1/FAILURE
Nov 21 12:23:42 ip-172-31-23-90 systemd[1]: nginx.service: Failed with result 'exit-code'.
Nov 21 12:23:42 ip-172-31-23-90 systemd[1]: Failed to start A high performance web server and a reverse proxy server.

The job identifier is 5626.
Nov 21 12:23:42 ip-172-31-23-90 nginx[21094]: nginx: [emerg] unknown directive "sten" in /etc/nginx/conf.d/default.conf:1
Nov 21 12:23:42 ip-172-31-23-90 nginx[21094]: nginx: configuration file /etc/nginx/nginx.conf test failed
Nov 21 12:23:42 ip-172-31-23-90 systemd[1]: nginx.service: Control process exited, code=exited, status=1/FAILURE
-- Subject: Unit process exited
-- Defined-By: systemd

I also checked the error log with "cat /var/log/nginx/error.log" and i got the following :

ubuntu@ip-172-31-23-90:~$ cat /var/log/nginx/error.log
2020/11/21 07:47:49 [emerg] 18846#18846: unknown directive "er" in /etc/nginx/nginx.conf:1
2020/11/21 07:54:57 [emerg] 18898#18898: unknown directive "er" in /etc/nginx/nginx.conf:1
2020/11/21 07:59:37 [emerg] 18924#18924: unknown directive "er" in /etc/nginx/nginx.conf:1
2020/11/21 11:09:41 [emerg] 20449#20449: unknown directive "er" in /etc/nginx/nginx.conf:1
2020/11/21 11:20:03 [emerg] 20485#20485: unknown directive "er" in /etc/nginx/nginx.conf:1
2020/11/21 11:52:44 [emerg] 20822#20822: unknown directive "sten" in /etc/nginx/conf.d/default.conf:1
2020/11/21 12:23:42 [emerg] 21094#21094: unknown directive "sten" in /etc/nginx/conf.d/default.conf:1