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<!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 class="w3-container">

<h2>Active Accordions</h2>
<p>In this example we add the w3-red class to an active accordion (when the button is clicked on and the content is opened).</p>

<div class="w3-accordion w3-light-grey">
  <button onclick="myFunction('Demo1')" class="w3-btn-block w3-left-align">Open Section 1</button>
  <div id="Demo1" class="w3-accordion-content w3-container">
      <p>Some text..</p>
  </div>
  <button onclick="myFunction('Demo2')" class="w3-btn-block w3-left-align">Open Section 2</button>
  <div id="Demo2" class="w3-accordion-content w3-container">
      <p>Some other text..</p>
  </div>
</div>

<script>
function myFunction(id) {
    var x = document.getElementById(id);
    if (x.className.indexOf("w3-show") == -1) {
        x.className += " w3-show";
        x.previousElementSibling.className += " w3-red";
    } else { 
        x.className = x.className.replace(" w3-show", "");
        x.previousElementSibling.className = 
        x.previousElementSibling.className.replace(" w3-red", "");
    }
}
</script>

</body>
</html>