reagent/examples/react-transition-group/resources/public/fade.css

.hide {
  opacity: 0.01;
}

.fade-enter {
  opacity: 0.01;
}

.fade-enter.fade-enter-active {
  opacity: 1;
  transition: opacity 500ms ease-in;
}

.fade-exit {
  opacity: 1;
}

.fade-exit.fade-exit-active {
  opacity: 0.01;
  transition: opacity 300ms ease-in;
}