chromium/third_party/blink/web_tests/inspector-protocol/css/resources/view-transition.css

#target {
  width: 100px;
  height: 100px;
  background-color: blue;
  view-transition-name: target;
}

::view-transition-group(root),
::view-transition-group(target) {
  animation-duration: 300s;
}

::view-transition-group(target) {
  opacity: 1;
}