How can i use Tailwind using Sass on Vue

Try to uninstall that dependencies which are related to postcss and tailwind :

npm uninstall tailwindcss postcss autoprefixer

then install them using the following command :

npm i -D tailwindcss@npm:@tailwindcss/postcss7-compat postcss@^7 autoprefixer@^9

according to this section

As of v2.0, Tailwind CSS depends on PostCSS 8. Because PostCSS 8 is only a few months old, many other tools in the ecosystem haven't updated yet

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