JSFiddle - React, Tailwind, and code Playground

HTML

<div id="vue">
  <div v-html="'<span>Hello!</span>'"></div>
  {{greeting}}
  <child ref="child"></child>
</div>

JavaScript

new Vue({
  el: '#vue',
  data: {
    greeting: 'Hello Vue!'
  },
  components: {
    child: {
      template: '<div><h1>Child content</h1></div>'
    }
  },
  mounted() {
    console.log(this.$el.outerHTML)
    console.log(this.$refs.child.$el.outerHTML)
  }
})