それを自分で試してみてください

<!DOCTYPE html>
<html>
<title>W3.CSS</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="/lib/w3.css">
<body>

<img src="img_fjords.jpg" alt="Fjords" style="width:100%">
  <a class="w3-red w3-padding" href="#">Home</a>
  <a class="w3-padding" href="#">Projects <span class="w3-tag w3-red w3-round w3-right">8</span></a>
  <a class="w3-padding" href="#">About</a>
  <a class="w3-padding" href="#">Contact</a>

<div class="w3-container w3-section">
    <div class="w3-border w3-round w3-padding w3-blue-grey">
      <span onclick="this.parentElement.style.display='none'" class="w3-closebtn">&times;</span>
      <p>Lorem ipsum box...</p>
    </div>
  </div>
</nav>

<div class="w3-container">
  <p>Add whatever you like inside the side navigation.</p>
</div>

</div>
      
</body>
</html>