Challenge 1: Fix a Div-Based Button — Possible Solution
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<button class="btn" onclick="submitForm()">Submit</button>

WHY THIS WORKS
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- Swapping <div> for <button> is the ONLY structural change needed —
  the class="btn" attribute (and whatever CSS styling it applies) and
  the onclick="submitForm()" handler both carry over unchanged, since
  neither of those has anything to do with the underlying semantic
  problem being fixed.
- This single change gives everything the chapter's comparison box
  described "for free": a screen reader now announces this as a
  "button" (the correct role), it's automatically included in the
  page's tab order (no manual tabindex needed), and it can be activated
  with either Enter or Space once focused — none of which the original
  <div> version provided, regardless of how convincingly it was styled
  to LOOK like a button.
- Choosing <button> specifically (rather than <a href>) is also the
  correct choice per this chapter's buttons-vs-links distinction:
  "Submit" performs an ACTION (submitting a form) rather than
  navigating to a different page or URL — exactly the case the chapter
  describes as belonging to <button>, not <a href>.
- No changes to the visual appearance are needed at all — the existing
  class="btn" CSS class continues to apply exactly the same styling
  the div previously had, since <button> is just as freely styleable as
  a <div> was; only its underlying semantics and default behaviors
  differ (in this case, differ for the better).