CSS anchor positioning

CSS for placing one element relative to another anywhere in the document — the target names an anchor (position-anchor: --trigger) and positions itself with anchor() values (top: anchor(bottom)), with position-try fallbacks that flip or shift it when it would leave the viewport — so tooltips, popovers and menus need no JavaScript to find their trigger

The last piece of the popover puzzle: the Popover API opens and closes the layer, anchor positioning puts it beside the button and keeps it on screen. Together they replace what Floating UI and Popper do — which is what Reka UI, under Nuxt UI, still uses today, and will until the CSS is Baseline (Chromium shipped it; Safari and Firefox are landing it). A position-try-fallbacks: flip-block is the whole “open upward when there is no room below” logic, in one declaration.