ExtractTextPlugin Sass Loader Error

Question

I am "webpack": "^1.14.0", "css-loader": "^0.26.1" "sass-loader": "^4.1.1" .

I see the console error

addStyles.js:147 Uncaught Error: Couldn't find a style target. This probably means that the value for the 'insertInto' parameter is invalid.
    at insertStyleElement (addStyles.js:147)
    at createStyleElement (addStyles.js:184)
    at addStyle (addStyles.js:251)
    at addStylesToDom (addStyles.js:116)
    at ../node_modules/style-loader/lib/addStyles.js.module.exports (addStyles.js:67)
    at Object../prompt.css (prompt.css?d8f8:12)
    at __webpack_require__ (bootstrap bbe7b5471983b5ec6c6f:19)
    at Object../prompt.js (prompt.js:17)
    at __webpack_require__ (bootstrap bbe7b5471983b5ec6c6f:19)
    at Object.3 (prompt.js:696)

Following is my webpack config file

let ExtractTextPlugin = require('extract-text-webpack-plugin');

  {
    test: /\.s?css$/,
    loader: ExtractTextPlugin.extract("style-loader", "css-loader!postcss-loader")
  },

 plugins: [
    new ExtractTextPlugin("css/styles.css", { allChunks: true })
  ]