Atom is not available in the way that is explained in module 2 unit 7. To handle html and css files notepad++ could be a good solution. I am trying VSCode with the extension Arduino (Microsoft), given access to inteliisense and it works well at least with exercises of Modules 1 and 2 of the course.
At the moment, we recommend using Vs Code with PlaformIO instead. I need to update that unit.
We have instructions on how to use it if you want to experiment: