W3Schools Tryit Editor

<!DOCTYPE html>
<html>
<body>

<details id="myDetails">
  <summary>Copyright 1999-2014.</summary>
  <p> - by Refsnes Data. All Rights Reserved.</p>
  <p>All content and graphics on this web site are the property of the company Refsnes Data.</p>
</details>

<p>Click the buttons to toggle between opening and closing the additional details. <b>Note:</b> This can also be achieved by clicking on the carat sign on the left side of the Copyright text.</p>

<button onclick="openDetails()">Open details</button>
<button onclick="closeDetails()">Close details</button>

<p><b>Note:</b> The details element is not supported in Internet Explorer or Safari 5 and earlier versions.</p>

function closeDetails() {
  document.getElementById("myDetails").open = false;
}
</script>

</body>

</html>