我尝试使用Animation Add-Ons添加动画，按照官方文档上示例，但是动画完全没有效，为什么？

jsx

import React from 'react'
import ReactCSSTransitionGroup from 'react-addons-css-transition-group'
import './login.css'

class login extends React.Component {
  render() {
    return (
      <div className="bg">
        <div className="rocket animated infinite bounce"></div>
        <div className="cloud"></div>
        <div className="cloud2"></div>
        <ReactCSSTransitionGroup
          transitionName="example"
          transitionEnterTimeout={1000}
          transitionLeaveTimeout={1000}>
          <div key="111">33333333333333</div>
        </ReactCSSTransitionGroup>
      </div>
    )
  }
}
export default login

css

.example-enter {
  color: #fff;
}

.example-enter.example-enter-active {
  color: #000;
  transition: color 1000ms ease-in;
}

.example-leave {
  opacity: 1;
}

.example-leave.example-leave-active {
  opacity: 0.01;
  transition: opacity 300ms ease-in;
}