How do I put the site into maintenance mode with a what's coming showcase?

Maintenance mode replaces the public site with a polished page while you work, and it can showcase what is coming. Go to Site settings and open Maintenance. Turn it on (optionally set a start and end time). Set the title, tagline and about text, and the theme colours. For the showcase, use the 'What's coming' slides: add slides with an icon, title and one-line description. They auto-rotate every 5 seconds on the public page, with clickable dots. You can also add a service grid and even a short video. Admins can still sign in while maintenance is on, so you keep working. Turn maintenance off to restore the normal site.