HTTP client & HTTP server rely on relatively lower layer TCP to transport HTTP message.

TCP is implemented on the OS.

The TCP on the OS of the web browser will create a connection with the TCP on the OS of the web server.

Protocol vs. Protocol Implementation

A protocol is NOT code, it’s a reference model, usually written in English.

An HTTP client/server implementation can be written in any language you choose. For example:

The standard implementation is written in C (Apache httpd) and there are other implementations of HTTP server in almost any language that is available.