At the very first you should learn and understand at least basic
that is provided before asking questions. Chances are that if you had done both, you wouldn’t even have landed here.
Now, the script must be applied to some kind of text. You just copied and pasted the demonstration code without changing the ID to which you want to apply the script. I don’t see any element called “responsive_headline” in your code. Also – another sign that you don’t even know what you are doing just yet – you didn’t even put the reference to the script itself in the document header so no wonder that nothing is happening.