Since [Single Page App] transitions are supported, and SPA navigation happens entirely in-page, a ‘page’ in this case is just any given state of the document. We can capture the state of things at one moment, define that as the starting page, make any changes we want, and define the results as our ending page –- then animate between them.
There’s a new web API proposal for transitioning shared-elements across pages. It’s great for making smooth page transitions, but what if we apply it to individual elements with changing styles on a single page?
Every Transition is a Page Transition?
Experimenting with the shared element transitions API
Repost from OddBird.net