Setup guide component modifies `document.body` classes (outside component) in a side effect - can this be avoided?

[ksere]

As discussed here

Need to justify why components need to affect the DOM outside the component (body classes etc) - this is unusual.

Ideally the component wouldn't need to modify anything on the page outside of the component. Hopefully there's a way to refactor this so the component is self-contained.

If this is unavoidable then it should be clarified in the code (comment / rationale).

[haszari]

The core issue here is that components should not be modifying the DOM outside the component. Retitling to clarify this is the actual issue.