Welcome text not aligning to the center ,why?

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MY HTML CODE,CSS CODE IS PROVIDED BY MDN:_>

<meta charset="utf-8">

<title>Birdwatching</title>

<link href="https://fonts.googleapis.com/css?family=Roboto+Condensed:300%7CCinzel+Decorative:700" rel="stylesheet">

<link href="style.css" rel="stylesheet">

<!--[if lt IE 9]>

  <script src="https://cdnjs.cloudflare.com/ajax/libs/html5shiv/3.7.3/html5shiv.js"></script>

<![endif]-->
  <h1>Birdwatching</h1>

  <img src="dove.png" alt="a simple dove logo">
  <ul>

    <li><span>Home</span></li>

    <li><a href="#">Get started</a></li>

    <li><a href="#">Photos</a></li>

    <li><a href="#">Gear</a></li>

    <li><a href="#">Forum</a></li>

  </ul>

</nav>
 <header>

  <h2>Welcome</h2>

 

  <p>Welcome to our fake birdwatching site. If this were a real site, it would be the ideal place to come to learn more about birdwatching, whether you are a beginner looking to learn how to get into birding, or an expert wanting to share ideas, tips, and photos with other like-minded people.</p>

  <p>So don't waste time! Get what you need, then turn off that computer and get out into the great outdoors!</p>

</article>
  <p>This fake website example is CC0 — any part of this code may be reused in any way you wish. Original example written by Chris Mills, 2016.</p>

  <p><a href="http://game-icons.net/lorc/originals/dove.html">Dove icon</a> by Lorc.</p>

</footer>