Archive and slide

Each email is an invisible slot in a plain list, with the visible card data-⚓️-fill on its slot and data-⚓️-transition="glide". Archiving only sets the slot's height to zero: the list reflows instantly, so the archived card's height glides shut and every card below glides up into its new position. The inbox panel behind them is anchored to the whole list too, so it shrinks with them. The script flips one attribute per click.