Vertical and right-to-left

orientation="vertical" scrolls along the block axis. A vertical deck needs a height, set on Deck.Viewport in CSS. Each slide fills it by default.

The deck reads the writing direction from the document's computed direction, so dir on any ancestor applies. In a right-to-left document the deck starts at the right, Next moves toward the inline end on the left, and a mouse drag and the arrow keys follow.

A deck follows a change of dir after it mounts, as after a locale switch. It stays on its slide and goes the new way from there. The deck does not watch a change of direction in CSS alone, and a deck inside a shadow root does not see a change of dir on its ancestors outside it.