<div id="demo" >
  <button @click="animate" >
    Click Me
  </button>
  <div :class='(animated) ? "animated" : ""  ' >
    <div>Lorem ipsum dolor sit amet consectetur adipisicing elit. Autem quam omnis repellat! Porro, nesciunt eos, quidem maiores pariatur debitis ut sapiente molestiae sint impedit odit dolorem, autem quos nam ducimus?</div>
  </div>
</div>
div {
  transition: all 0.2s;
}
div.animated {
  background: #333;
  color: white;
  font-family: Arial;
  line-height: 2;
  padding: 10px;
  transition: all 0.2s;
}
new Vue({
  el: "#demo",
  data: {
    animated: false,
  },
  methods: {
    animate: function ()  {
      this.animated = !this.animated;
    }
  }
});
Rerun