chromium/third_party/blink/web_tests/external/wpt/html/semantics/popovers/resources/popover-styles.css

.fake-popover {
  position: fixed;
  inset: 0;
  width: fit-content;
  height: fit-content;
  margin: auto;
  border: solid;
  padding: 0.25em;
  overflow: auto;
  color: CanvasText;
  background-color: Canvas;
}
.fake-popover[anchor] {
  inset: auto;
}
.fake-popover-backdrop {
  position: fixed;
  inset:0;
  pointer-events: none !important;
}