Add kiosk.js file with the content below to your www folder in config.
Like any other custom script, use ui-lovelace.yaml resources section to reference the kiosk.js file.
Make sure you add kiosk somewhere in your URL. You can use it in the id of your view or in the query string.
Examples:
/lovelace/0?kiosk
views:
- title: Kiosk
icon: mdi:heart
id: kiosk_alarmIf this is your first file in www make sure you restart Home Assistant.

More on this. I discovered that I can change style.display for the header from "none" to "block" and it will appear. However, because it draws the header before the tabs disappear, it leaves a space. But the odd part (to me, at least): if I click on a header tab to change the view, the header corrects itself. Here are "before" and "after" images. First, the before:

Now, the after: