sphinx_rtd_theme/webpack.common.js

const path = require('path');
const MiniCssExtractPlugin = require('mini-css-extract-plugin');

module.exports = {
  entry: './src/index.js',
  output: {
    filename: 'js/theme.js',
    path: path.resolve(__dirname, 'sphinx_rtd_theme/static')
  },
  module: {
    rules: [
      {
        test: require.resolve('./src/theme.js'),
        use: 'imports-loader?this=>window'
      },
      {
        test: /\.sass$/,
        use: [{
          loader: MiniCssExtractPlugin.loader
        }, {
          loader: "css-loader"
        }, {
          loader: "sass-loader?indentedSyntax",
          options: {
            includePaths: [
              'node_modules/bourbon/app/assets/stylesheets',
              'node_modules/bourbon-neat/app/assets/stylesheets',
              'node_modules/font-awesome/scss',
              'node_modules/wyrm/sass'
            ]
          }
        }]
      },
      {
        test: /\.(woff(2)?|ttf|eot|svg)(\?v=\d+\.\d+\.\d+)?$/,
        use: [{
          loader: 'file-loader',
          options: {
            name: '[name].[ext]',
            outputPath: 'fonts/',
            publicPath: '/_static/fonts',
          }
        }]
      }
    ]
  },
  plugins: [
    new MiniCssExtractPlugin({
      // Options similar to the same options in webpackOptions.output
      // both options are optional
      filename: 'css/theme.css'
    })
  ]
};