You can also click "Add to calendar" and download the ics file. Open that file and you can then accept the invitation. The download file includes the link to join (2am our time). It would be good if the info at the top of the page included a link to view the time in your timezone (you can create those links in sites like timeanddate.com).

After logging in, I was presented with a button above to RSVP for the event. It will be online at the 'Join' URL provided in the banner above.