node.js – web application using nginx and node – what is the web server?

I have a web application that uses nginx as a reverse proxy and that uses the express framework as my backend in node.js. I'm confused about what the web server is, maybe both or maybe it's a gray area in my case. I use to react, so the application presents the representation on the client side, and nginx maintains these files in case it makes a difference.

According to developer.mozilla.org

On the software side, a web server includes several parts that control how web users access the hosted files, at least one HTTP server. An HTTP server is a piece of software that includes URLs (web addresses) and HTTP (the protocol your browser uses to view web pages). It can be accessed through the domain names (such as mozilla.org) of the websites it stores, and delivers its content to the end user's device.

Y

A web server must first store the files of the website, that is, all HTML
documents and their related assets, including images, CSS style sheets,
JavaScript files, fonts and videos.

Bearing this in mind, I would say that Nginx is the web server, since it contains the html file. However, I'm really not sure. Is it one of the two, or is it a gray area?