JSFiddle - React, Tailwind, and code Playground

HTML

<script src="//unpkg.com/vue/dist/vue.js"></script>
<script src="//unpkg.com/element-ui/lib/index.js"></script>
<div id="app">
  <el-menu :default-active="activeIndex">
    <el-menu-item :index="item.id" v-for="(item, index) in menus" :key="item.id">
      {{item.label}}
    </el-menu-item>
  </el-menu>
</div>

CSS

@import url("//unpkg.com/element-ui/lib/theme-default/index.css");

#app .el-menu .el-menu-item.is-active{
  background-color: #d1dbe5;
}

JavaScript

var Main = {
  data() {
    return {
      activeIndex: '1',

      menus: [{
        id: '1',
        label: 'aaa'
      },{
        id: '2',
        label: 'bbb'
      },{
        id: '3',
        label: 'ccc'
      }]
    }
  }
}
var Ctor = Vue.extend(Main)
new Ctor().$mount('#app')