W3Schools Tryit Editor

<!DOCTYPE html>
<html lang="en">
<title>W3.CSS Case</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://www.w3schools.com/w3css/5/w3.css">
<body>

<nav class="w3-sidebar w3-bar-block w3-black w3-card w3-large" style="display:none" id="mySidebar">
  <a href="javascript:void(0)" onclick="w3_close()" 
  class="w3-button w3-black w3-right">&times;</a><br>
  <a class="w3-bar-item w3-button" href="#">Link 1</a>
  <a class="w3-bar-item w3-button" href="#">Link 2</a>
  <a class="w3-bar-item w3-button" href="#">Link 3</a>
</nav>

<header class="w3-light-grey">
  <button class="w3-button w3-light-grey w3-xxlarge" onclick="w3_open()">&#9776;</button>
  <div class="w3-container">
  <h1 class="w3-jumbo">My First W3.CSS Website!</h1>
  <p class="w3-xlarge">This site will grow as we add more ...</p>
  </div>
</header>

<div class="w3-row-padding">
  <div class="w3-quarter">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.</p>
  </div>
  <div class="w3-half">        
  <p><strong>On a large screen the content will be displayed as a 3-column layout. On a small screen the content will adjust itself into a single-column. Resize the browser window to see the effect.</strong></p>
  </div>
  <div class="w3-quarter">        
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.</p>
  </div>
</div>

<footer class="w3-container w3-light-grey">
  <p>This is my footer</p>
</footer>

</body>
</html>

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<!DOCTYPE html><html lang="en"><title>W3.CSS Case</title><meta name="viewport" content="width=device-width, initial-scale=1"><link rel="stylesheet" href="https://www.w3schools.com/w3css/5/w3.css"><body>​<nav class="w3-sidebar w3-bar-block w3-black w3-card w3-large" style="display:none" id="mySidebar">  <a href="javascript:void(0)" onclick="w3_close()"   class="w3-button w3-black w3-right">&times;</a><br>  <a class="w3-bar-item w3-button" href="#">Link 1</a>  <a class="w3-bar-item w3-button" href="#">Link 2</a>  <a class="w3-bar-item w3-button" href="#">Link 3</a></nav>​<header class="w3-light-grey">  <button class="w3-button w3-light-grey w3-xxlarge" onclick="w3_open()">&#9776;</button>  <div class="w3-container">  <h1 class="w3-jumbo">My First W3.CSS Website!</h1>  <p class="w3-xlarge">This site will grow as we add more ...</p>  </div></header>​<div class="w3-row-padding">  <div class="w3-quarter">    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.</p>  </div>  <div class="w3-half">        