JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://unpkg.com/vue"></script>

<div id="demo">
  <button v-on:mouseenter="show = !show" v-on:mouseleave="show = !show">
    Toggle
  </button>
  <transition name="fade">
    <p>hello</p>
  </transition>
</div>

CSS

.fade-enter-active, .fade-leave-active {
  opacity: .5;
  transition: all .5s
}
.fade-enter, .fade-leave-to /* .fade-leave-active in <2.1.8 */ {
  opacity: 1
}

JavaScript

new Vue({
  el: '#demo',
  data: {
    show: true
  }
})