App.vue

<template>
    Main Layout
    <RouterView />
</template>

<script setup>
import { RouterView } from 'vue-router'
</script>

<style>
html {
    @apply bg-gray-800;
}
</style>

main.css

@tailwind base;
@tailwind components;
@tailwind utilities;

main.js

import { createApp } from 'vue'
import { createPinia } from 'pinia'
import './assets/main.css'

import App from './App.vue'
import router from './router'

const app = createApp(App)

app.use(createPinia())
app.use(router)

app.mount('#app')

tailwind.config.js

/** @type {import('tailwindcss').Config} */
export default {
  content: [
    "./src/index.html",
    "./src/**/*.{vue,js}"
  ],
  theme: {
    extend: {},
  },
  plugins: [],
}