Accessibility
useContainerQueries changes column count, ensure content reflow does not strand interactive controls off-screen.
A subgrid changes only which tracks a nested Grid's children sit on. The nested Grid keeps its element and role, so an article card or a labelled section keeps its name, unlike a display: contents wrapper. Cards still read card by card in DOM order, even when their parts line up across a row.
Area layouts. DOM order must match the logical reading and focus order, which is the order of the narrowest (single-column) layout. Area layouts may rearrange children visually only in ways that keep that order sensible; they never change what a screen reader or the Tab key meets first. defineGridAreas records the order as readingOrder; put the children in that order.