Example resources/js/App.vue and resources/js/App.vue file for a laravel+vue project. The main.js file in a VueCLI project is our app.js. I kept the app.js name from a default laravel project.

app.js

import Vue from 'vue'
import App from './App.vue'
import router from './router'
import store from './store'
import vuetify from './vuetify'
import Vuelidate from 'vuelidate'
Vue.use(Vuelidate)

Vue.config.productionTip = false
const app = new Vue({
  router,
  store,
  vuetify,
  render: h => h(App)
}).$mount('#app')

App.vue

<template>
  <v-app>
    <left-menu/>
    <header-component/>
    <v-content>
      <router-view/>
    </v-content>
    <footer-component/>
  </v-app>
</template>

<script>

import HeaderComponent from './components/HeaderComponent'
import FooterComponent from './components/FooterComponent'
import LeftMenu from './components/LeftMenu'
export default {
    components: {
      LeftMenu,
      FooterComponent,
      HeaderComponent,
    },
}
</script>

<style >

h1, h2, h3, p, span, div {
  font-family: 'DDINRegular', Courier, monospace;
}

</style>