JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.3/vue.min.js"></script>

<div id="app">
  <input v-model="fontSize" type="range">
  <h1 v-for="n in items">{{ n }}</h1>
</div>

CSS

h1 {
  font-size: var(--h1-font-size);
}

JavaScript

new Vue({
  el: '#app',
  data: () => ({
    fontSize: 24,
    items: [ 'hello, world!!', 'fuck the world', 'fuck everything' ],
  }),
  mounted() {
    this.$watch(
      'fontSize',
      val => this.$el.style.setProperty('--h1-font-size', `${val}px`),
      { immediate: true }
    );
  },
});