Created attachment 476783 [details] A recording of the bug in Safari on the left and Chrome on the right Overview: When popover elements are transitioning into their closed state (using transition-behavior: allow-discrete), they lose their top-layer benefits (such as "position" and "z-index" isolation). Demo: The following Codepen shows that an element with position:relative is able to overlap the popover element while the popover is transitioning into a closed state, regardless of the top-layer benefits that it's meant to have. The demo uses anchor-positioning to accurately position the popover, but this bug happens with non-anchored popovers too. https://codepen.io/eharber/pen/emJOwxx?editors=1100 A screen recording showing Safari on the left and Chrome on the right has been attached. Expected Results: During the closing transition, the popover should stay on top of all other elements. This occurs on the latest versions of Safari (26.0) and Safari TP (228) This bug is isolated to WebKit. Chromium browsers handle this transition correctly.