Challenge 2: Applying a Fill That Doesn't Appear to Do Anything — Solution Walkthrough

The answer:

Per this chapter's own material on open vs. closed paths, a fill needs
a closed path — one whose last anchor point connects back to its
first, forming a continuous loop with an actual interior area to
color. The most likely cause here is that the path was left open: the
last anchor point was never clicked back onto the starting point, so
the shape has no enclosed interior for the fill to occupy.

Why this specific symptom (fill applied, nothing visible) points to an
open path:

An open path can technically have a fill setting applied to it, but
without a closed loop there's no bounded interior area for that fill
to actually render into, which is why nothing visibly changes even
though the fill was applied correctly.

What fixes it:

Reopening the path for editing and clicking the final anchor point
back onto the starting point closes the loop, giving the fill an
actual interior region to color.

WHY THIS WORKS AS AN ANSWER
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This exercise checks that a fill with no visible effect is correctly
diagnosed as an open path lacking an enclosed interior, rather than a
tool malfunction or an unrelated setting.