<div id="app">
  <button @click="show = !show" :aria-expanded="show ? 'true' : 'false'">
    Toggle Panel
  </button>
  <p v-if="show">hello</p>
</div>
#app {
  margin: 50px;
}

p {
  padding: 10px 12px;
  border: 1px solid #ccc;
  width: 100px;
}
new Vue({
  el: '#app',
  data: {
    show: true
  }
})

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

  1. https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.13/vue.js