The ::view-transition-image-pair CSS pseudo-element represents a container for a view transition's "old" and "new" view states — before and after the transition.
During a view transition, ::view-transition-image-pair is included in the associated pseudo-element tree as explained in The view transition pseudo-element tree. It is only ever a child of a ::view-transition-group. In terms of children, it can have a ::view-transition-new or a ::view-transition-old, or both.
::view-transition-image-pair is given the following default styling in the UA stylesheet:
:root::view-transition-image-pair(*) {
position: absolute;
inset: 0;
animation-duration: inherit;
animation-fill-mode: inherit;
animation-delay: inherit;
}
During a view transition, ::view-transition-image-pair has isolation: isolate set on it in the view transition style sheet so that its children can be blended with non-normal blend modes without affecting other visual outputs.