title: The output from the postcss webpack does not display the css prefix
body: <p>I have problem with prefixer in webpack 5 bundler.
  After proper implementation, not all prefix requirements are created for me.</p>
  <p>I work with SASS, so all input files are .scss, I am attaching an excerpt from webpack.config.js:</p>
  <pre><code>const path = require('path');
  const { CleanWebpackPlugin } = require('clean-webpack-plugin');
  const HtmlWebpackPlugin = require('html-webpack-plugin');
  const { merge } = require('webpack-merge');
  const MiniCssExtractPlugin = require(&quot;mini-css-extract-plugin&quot;);
  const purgecss = require('@fullhuman/postcss-purgecss');
  const dir = path.resolve(__dirname, '.');
  
  const productionConfig = {
  
      optimization: {
          splitChunks: {
            cacheGroups: {
              styles: {
                name: 'styles',
                test: /\.css$/,
                chunks: 'all',
                enforce: true
              }
            }
          }
        },
  
      module: {
          rules: [
            {
              test: /\.m?js$/,
              exclude: /(node_modules|bower_components)/,
              use: {
                loader: 'babel-loader',
                options: {
                  presets: ['@babel/preset-env']
                }
              }
            },
            {
              test: /\.s[ac]ss$/i,
              use: [
                MiniCssExtractPlugin.loader,
                &quot;css-loader&quot;,
                &quot;postcss-loader&quot;,
                &quot;sass-loader&quot;
              ],
            },
          ]
        },
  
        plugins: [
          new MiniCssExtractPlugin({
          filename: '[name].[chunkhash:8].css',
          chunkFilename: &quot;[id].css&quot;
          }),
      ],
  };
  </code></pre>
  <p>The output from my dev webpack json is:</p>
  <pre><code>asset index.html 355 bytes [emitted]
  asset main.2d6b3b71.css 139 bytes [emitted] [immutable] (name: main)
  asset main.2d6b3b71.js 0 bytes [emitted] [immutable] [minimized] (name: main)   
  Entrypoint main 139 bytes = main.2d6b3b71.css 139 bytes main.2d6b3b71.js 0 bytes
  orphan modules 3.02 KiB (javascript) 937 bytes (runtime) [orphan] 9 modules     
  cacheable modules 60 bytes (javascript) 138 bytes (css/mini-extract)
    ./src/js/app.js 60 bytes [built] [code generated]
    css ./node_modules/css-loader/dist/cjs.js!./node_modules/postcss-loader/dist/cjs.js!./node_modules/sass-loader/dist/cjs.js!./src/scss/base.scss 138 bytes [built] [code generated]
  webpack 5.61.0 compiled successfully in 4035 ms
  
  </code></pre>
  <p>Everything will happen to me without the slightest mistake. The problem, however, is that it doesn't add prefixes to me. Thus, matters such as:</p>
  <pre><code>::placeholder {
      color: #bada55;
  }
  
  body {
      display: grid;
  }
  
  </code></pre>
  <p>They tell me that the placeholder does not appear at all and the grid appears without prefixes.</p>