slide-transition-defaults-to-half-a-height

A vertical slide transition defaults to HALF the element's height, so it appears already halfway through its own movement and the first part is missing — which reads as a pop, not a slide. Covers passing the full height, the sign that decides which edge it comes from, pairing a shorter fade with a longer slide so the element is opaque before it settles, making exit quicker than enter, and publishing the pair as…