We’re very sorry that we’ll be causing this breakage, and we’d avoid it if we could - if there was a way to easily support existing CSS with our new architecture, we’d do that, but unfortunately there isn’t.
This kind of rearchitecture change is exactly the reason why we always made it clear that custom CSS can break. We’re only doing this because it allows us to make Glide better and faster.
Also, to clear up a potential misunderstanding: we’re not disabling custom CSS. It’ll still be possible, but the CSS that works now with current Apps won’t work with Apps in a few weeks anymore because the DOM structure will change.