The first few FCC projects include several user stories like this:
“User Story #1: My tribute page should have an element with a corresponding id=“main”, which contains all other elements.”
Build a tribute page
In these first few projects, I think FCC should get students into good habits by pushing them towards using classes rather than IDs as much as possible. The reasons why are laid out here by Harry Roberts: The Specificity graph
Clearly in these initial small projects, using IDs rather than classes won’t cause any problems at all. But still we should be encouraging students to keep the specificity of their CSS as low as possible from day one, I think.