I just spent 30 minutes trying to figure out why I couldn’t get Lesson 1_2_Hello_World_Web_Server (Server Files from Filesystem) to work.

Pages 172 & 173 says….

“Then, select the newly created data folder and create two files inside by clicking on
the New File icon.

One file should be called main.html and the other style.css.
You can give these files any other names as long and they have the .html and .css
extensions. However, we recommend using these exact names, otherwise you also
need to change the main.cpp file to make the web server work.”

However, mine would only work by naming the .html file

index.html

The PDF book source code for main.cpp has it ‘index.html’, do does the main.cpp in the downloadable resource.