NgmdAccordionItem

Disclosure / accordion item. Signal-driven open/close state, full ARIA (aria-expanded, aria-controls, region role + aria-labelledby).

Chevron: single down-arrow icon, rotated 180deg on open. 200ms ease.

Body: outer wrapper is a CSS grid container animating grid-template-rows from 0fr (closed) to 1fr (open) over 280ms. Inner wrapper has overflow: hidden + min-height: 0 so the row fr basis drives height. Works in Chrome 117+, Safari 17.4+, Firefox 121+.

prefers-reduced-motion zeroes all transitions.