Change your dependencies

[khoipro]

Your dependencies are below:

    "@fullhuman/postcss-purgecss": "^1.2.0",
    "autoprefixer": "^9.7.3",
    "cross-env": "^6.0.3",
    "laravel-mix": "^5.0.0",
    "postcss-import": "^12.0.1",
    "postcss-nested": "^4.2.1",
    "tailwindcss": "^1.1.4"

When running npm run development, you missed browser-sync package.

Some packages should move to devDependencies, like postcss-*, cross-ev, autoprefixer.