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<!DOCTYPE html> <html> <body> <h2 class="example">A heading with class="example"</h2> <p class="example">A paragraph with class="example".</p> <p>Click the button to add a background color to the first element in the document with class="example" (index 0).</p> <button onclick="myFunction()">Try it</button> <p><strong>Note:</strong> The querySelectorAll() method is not supported in Internet Explorer 8 and earlier versions.</p> <script> function myFunction() { var x = document.querySelectorAll(".example"); x[0].style.backgroundColor = "red"; } </script> </body> </html>