Vue 2.0 Hello World

HTML

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

<div id="demo">
  <button v-on:click="show = !show">
    Toggle
  </button>
  <transition name="fade-overlay">
    <div class="overlay" v-if="show"></div>
  </transition>
</div>

CSS

.overlay {
  width: 50px;
  height: 50px;
  background-color: red;
  opacity: 0.5;
}
.fade-overlay-enter,
.fade-overlay-leave-to {
  opacity: 0;
}
.fade-overlay-enter-active,
.fade-overlay-leave-active {
  transition: opacity 2s;
}

JavaScript

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