We have seen a few different button morphing to email form/push notification field, etc, this is another take on it designed by Danny Iovane. Great when you have limited space to play around with on your web page, you can use this button to reveral the email form on click.
If you are having trouble with the pen, try the archived copy on GitHub
Button to Email Notification Snippet
See the Pen Notify Me by Danny Iovane (@gingerdude) on CodePen.0