No PostCSS config found

If you don't want to add another file, it's enough to add your options in your webpack config:

         {
           loader: `postcss-loader`,
           options: {
             options: {},
           }
         },

you can use this if don't want to add a new config file.

         {
            loader: `postcss-loader`,
            options: {
              options: {},
            }
          },

this is the example of using MiniCssExtractPlugin at the same time.

module:{
    rules: [
      {
        test: /\.(sa|sc|c)ss$/,
        use: [
          {
            loader: MiniCssExtractPlugin.loader,
            options: {
              publicPath: (resourcePath, context) => {
                return path.relative(path.dirname(resourcePath), context) + '/';
              },
              hmr: process.env.NODE_ENV !== 'production',
            },
          },
          'css-loader',
          {
            loader: `postcss-loader`,
            options: {
              options: {},
            }
          },
          'sass-loader',
        ],
      },
    ],
  },

Here is a bigger snippet of kontrollanten's answer to be sure where exactly to place it:

module: {
    rules: [
        {
            test: /\.(scss)$/,
            resolve: { extensions: [".scss"], },
            use: [
                MiniCssExtractPlugin.loader,
                'css-loader',
                {
                    loader: `postcss-loader`,
                    options: {
                        options: {},
                    }
                },
                'resolve-url-loader?sourceMap',
                'sass-loader?sourceMap',
            ]
        }
    ],
},

Made a new file in the root directory named postcss.config.js and added

module.exports = {};

Found this on the following post:

https://stackoverflow.com/a/41758053/5350097