Edit in JSFiddle

<!-- template for the modal component -->
<script type="x/template" id="modal-template">
  <div class="modal-mask" v-show="show" transition="modal">
    <div class="modal-wrapper">
      <div class="modal-container">

        <div class="modal-header">
          <slot name="header">
            default header
          </slot>
        </div>
        
        <div class="modal-body">
          <slot name="body">
            default body
          </slot>
        </div>

        <div class="modal-footer">
          <slot name="footer">
            default footer
            <button class="modal-default-button"
              @click="show = false">
              OK
            </button>
          </slot>
        </div>
      </div>
    </div>
  </div>
</script>

<!-- app -->
<div id="app">
  <button id="show-modal" @click="showModal = true">Show Modal</button>
  <!-- use the modal component, pass in the prop -->
  <modal :show.sync="showModal">
    <!--
      you can use custom content here to overwrite
      default content
    -->
    <h3 slot="header">custom header</h3>
  </modal>
</div>
// register modal component
Vue.component('modal', {
  template: '#modal-template',
  props: {
    show: {
      type: Boolean,
      required: true,
      twoWay: true    
    }
  }
})

// start app
new Vue({
  el: '#app',
  data: {
    showModal: false
  }
})
.modal-mask {
  position: fixed;
  z-index: 9998;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-color: rgba(0, 0, 0, .5);
  display: table;
  transition: opacity .3s ease;
}

.modal-wrapper {
  display: table-cell;
  vertical-align: middle;
}

.modal-container {
  width: 300px;
  margin: 0px auto;
  padding: 20px 30px;
  background-color: #fff;
  border-radius: 2px;
  box-shadow: 0 2px 8px rgba(0, 0, 0, .33);
  transition: all .3s ease;
  font-family: Helvetica, Arial, sans-serif;
}

.modal-header h3 {
  margin-top: 0;
  color: #42b983;
}

.modal-body {
  margin: 20px 0;
}

.modal-default-button {
  float: right;
}

/*
 * the following styles are auto-applied to elements with
 * v-transition="modal" when their visiblity is toggled
 * by Vue.js.
 *
 * You can easily play with the modal transition by editing
 * these styles.
 */

.modal-enter, .modal-leave {
  opacity: 0;
}

.modal-enter .modal-container,
.modal-leave .modal-container {
  -webkit-transform: scale(1.1);
  transform: scale(1.1);
}