Now that the (live:) macro has been altered to internally work the same way as the (after:) and (event:) macros, and as the applying of that specific styling only needs to be done one even if other content is dynamically updated, I would use a slightly different set of macro calls…
I used to be a $type (after: 3s)[{
(change: ?Page, (bg: black) + (color: white))
until I wasn't
}]
note: Collapsing whitespace markup has only been added to the above example so that it can be formatted to make the code a little easier to read. That formatting and markup can be remove.