@starting-style — entry animations without JS
Click Add card, then flip the toggle off and add another. Same transition,
same markup — the only difference is whether @starting-style gives the browser
a "before" state to animate from.
Turn the toggle off to see the old problem: without a "before" state, a new card
can only jump straight to its final look — there is nothing for transition
to animate from.
Each card is a genuinely new DOM element — no fade class added a tick after mount.
Click the ✕ on a card to dismiss it (a normal transition; @starting-style only
ever applies to how something first appears, never to how it leaves).
This element is display: none until opened. transition-behavior: allow-discrete
lets display itself join the transition, so the fade-in isn't instant.