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<!DOCTYPE html> <html> <head> <style> .democlass { color: red; } </style> </head> <body> <h1>Hello World</h1> <p>Click the button to add a class attribute with the value of "democlass" to the h1 element.</p> <button onclick="myFunction()">Try it</button> <script> function myFunction() { document.getElementsByTagName("H1")[0].setAttribute("class", "democlass"); } </script> </body> </html>