ReactCSSTransitionGroup: transitionAppear doesn't work

Question

I'm trying to appearance/disappearance the notification, but transitionAppear doesn't work. I add item (notification popup) to the onBlur event. Animation at the time of leave works smoothly and at the time of appear it just appears abruptly without transition. In the React recently, do not swear strongly:D

P.S.
If I add ReactCSSTransitionGroup in alert.js -appear works, but leave - no.

CodeSandbox: https://codesandbox.io/s/l26j10613q
(on CodeSandbox I used ReactCSSTransitionGroup in alert.js, so appear works, but leave — no)

alert.js:

export default class Alert extends Component {
  render() {
    const { icon, text } = this.props;
    let classNames = "cards-wrapper-alert";
    return (
     <div className={classNames}>
       <Card zIndex="2">
         <Icon icon={icon} eClass="alert-message-icon"/>
         <Label text={text} fw="fw-medium" fs="fs-14" fc="c-dark"/>
       </Card>
     </div>
    );
  }
}

alert.css:

.alert-appear {
  max-height: 0;
  overflow: hidden;
}

.alert-appear.alert-appear-active {
  max-height: 80px;
  transition: max-height 300ms ease-in-out;
}

.alert-leave {
  max-height: 80px;
}

.alert-leave.alert-leave-active {
  max-height: 0;
  overflow: hidden;
  transition: max-height 300ms ease-in-out;
} 

What I do in input.js:

<ReactCSSTransitionGroup
  component={this.prepareComponentForAnimation}
  transitionName="alert"
  transitionEnter={false}
  transitionAppear={true}
  transitionAppearTimeout={400}
  transitionLeaveTimeout={400}>
    {this.state.alert ?
      <Alert icon={this.state.icon} text={this.state.text}/>
    : null}
</ReactCSSTransitionGroup> 

Example:

Answer 1

I had to change your code to reproduce the exact scenario that you've shown in your .gif, by moving ReactCSSTransitionGroup to the Input component.

After reading the docs, I found this line which makes sense as to why your Alert was not animating when showing up for the first time:

ReactCSSTransitionGroup provides the optional prop transitionAppear, to add an extra transition phase at the initial mount of the component.

What is happening here is not the initial mount. The alert state is set once there is some user interaction on the input.

So, the simple answer to your question is that you need to use the enter phase, and not appear phase because of the docs that I've posted above.