Hi Linda ,
Thank you for letting us know you're using Divi pop-up. Unfortunately, we currently do not support this pop up out-of-the-box, but you can still use the
Website URL button action.
If you enter just
#popup1, you will see a red warning message, but you can ignore that. The button will still execute the URL.
If you want to use the classname, that's possible with Buttonizer Pro. There you're able to add a custom class to a button.
Let me know if this helps 🙂