By default running Vite from npm command npm run dev, current dir will be served as root of the application.

There's cases where the current dir was not the root or where the index file live, for example this dir structure where npm init dir project_dir was the main project dir and the subdir src was the deployment output folder.

project_dir
    package.json
    vite.config.js
        src/
            index.html

In such cases, to change the default serving root dir we can explicitly specify the root dir inside vite.config.js.

If the file didn't exist, create it and define the root dir inside.

import { defineConfig } from 'vite';

export default defineConfig({
  root: './src/', 
});

The path ./src/ was relative to the package.json which contain the wrapping for Vite command.

{
  "name": "vite",
  "private": true,
  "version": "0.0.0",
  "type": "module",
  "scripts": {
    "dev": "vite",
    "build": "vite build",
    "preview": "vite preview"
  },
  "devDependencies": {
    "autoprefixer": "^10.4.14",
    "postcss": "^8.4.24",
    "tailwindcss": "^3.3.2",
    "vite": "^4.3.9"
  }
}

References

https://vitejs.dev/config/shared-options.html#base