postcss/Tailwind: Unused CSS selectors not purged

[a-0-dev]

I'm starting to use svelte-preprocess with webpack and tailwindcss. When running the dev server, warnings about unused CSS selectors appear, such as the following one:

WARNING in ./src/App.svelte
Module Warning (from ./node_modules/svelte-loader/index.js):
Unused CSS selector "video" (371:0)
369: img,
370: svg,
371: video,
     ^
372: canvas,
373: audio,
 @ ./src/main.ts 2:0-31 3:16-19

The problem is that one of these warnings appears for EVREY selector (~1500 lines of warnings), and of course there is also the warning overlay in the dev server's website view.

Technically, the combination Svelte+Webpack+TypeScript+TailwindCSS is already working for me (styling is applied etc.), it's just this mess of warnings that is a problem.

I could not yet find any explanation or fix on the internet, both because most documentation is for rollup, and because the postcss option for sveltePreprocess does not seem to have an option for purging unused CSS - at least I couldn't find anything.

If you need any more info on config files etc. I'm happy to provide them.

Excerpt from webpack.config.js:

module: {
    rules: [
      {
        test: /\.ts$/,
        loader: 'ts-loader',
        exclude: /node_modules/,
      },
      {
        test: /\.svelte$/,
        use: {
          loader: 'svelte-loader',
          options: {
            compilerOptions: {
              dev: !prod,
            },
            emitCss: prod,
            hotReload: !prod,
            preprocess: sveltePreprocess({ 
              sourceMap: !prod,
              postcss: {
                plugins: [
                  tailwindcss, 
                  autoprefixer
                ],
              },
            }),
          },
        },
      },
      {
        // required to prevent errors from Svelte on Webpack 5+
        test: /node_modules\/svelte\/.*\.mjs$/,
        resolve: {
          fullySpecified: false,
        },
      },
    ],
  },

Whole tailwind.config.js:

module.exports = {
    content: [
      './src/**/*.svelte',
      './src/**/*.html',
      './public/index.html',
    ],
    theme: {
      extend: {},
    },
    plugins: [],
  }

[josbra-attensi]

Also experienced this now working in Svelte with Tailwind, set the style tag lang to "postcss" so I can use tailwind directives, and now I have a bunch of diagnostics for every css selector I haven't used in this file

[vincaslt]

it almost seems like svelte preprocess runs after postcss plugins, because even adding cssnano does nothing to remove these (unused) comments.