Screen reader and landmark help

I can’t do the last step: to make sure the header element has a closing tag:


  <header>
    <h1>Training with Camper Cat</h1>
  <nav/>


  <main>
    <section id="stealth">

      <h2>Stealth &amp; Agility Training</h2>
      <article><h3>Climb foliage quickly using a minimum spanning tree approach</h3></article>
      <article><h3>No training is NP-complete without parkour</h3></article>
    </section>
    <section id="combat">

      <h2>Combat Training</h2>
      <article><h3>Dispatch multiple enemies with multithreaded tactics</h3></article>
      <article><h3>Goodbye world: 5 proven ways to knock out an opponent</h3></article>
    </section>
    <section id="weapons">
      <h2>Weapons Training</h2>
      <article><h3>Swords: the best tool to literally divide and conquer</h3></article>
      <article><h3>Breadth-first or depth-first in multi-weapon training?</h3></article>
    </section>
  </main>
</body>```

You have an opening header tag, with no closing tag.