SPA transitions

.header h1 {
  view-transtion-name: header;
}

::view-transition
├─ ::view-transition-group(root)
│  └─ ::view-transition-image-pair(root)
│     ├─ ::view-transition-old(root)
│     └─ ::view-transition-new(root)
└─ ::view-transition-group(header)
   └─ ::view-transition-image-pair(header)
      ├─ ::view-transition-old(header)
      └─ ::view-transition-new(header)