How to add CSS configuration in reactjs Project?

As per our chat, this is what your webpack.config.js file is as below:

var path = require("path"); 

var DIST_DIR = path.resolve(__dirname, "dist"); 
var SRC_DIR = path.resolve(__dirname, "src"); 

var config = { 
  entry: SRC_DIR + "/app/index.js", 
  output: { 
    path: DIST_DIR + "/app", 
    filename: "bundle.js", 
    publicPath: "/app/" 
  }, 
  module: { 
    loaders: [ 
      { 
        test: /\.js?/, 
        include: SRC_DIR, 
        loader: "babel-loader", 
        query: { 
          presets: ["react", "es2015", "stage-2"] 
        }
      } 
      { 
        test: /\.css$/, 
        loaders: ["style-loader", "css-loader", "sass-loader"] 
      } 
      { 
        test: /\.less$/, 
        loader: ExtractTextPlugin.extract("css-loader!sass-loader") 
      } 
    ] 
  }, 
  plugins: [ 
    new ExtractTextPlugin("src/components/assets/css/style.css", { 
      allChunks: true 
    }) 
  ] 
}; 

module.exports = config;

There are two issues with this config.

1. The are no commas separating the loaders objects.
2. You are using ExtractTextPlugin but have not imported/required it anywhere in the config.

Issue #1 is quite obvious how to solve; simply add the commas after each definition of a loader object.

Issue #2 as well, you need to install and reference ExtractTextPlugin in you webpack config file.

You can do so by running the following command in your terminal:

npm install --save-dev extract-text-webpack-plugin

This will install the plugin to your node_modules and also list it in your package.json file under thedevDependencies` object.

And then in your webpack.config.js where you are requiring modules, also require the plugin like so:

const ExtractTextPlugin = require("extract-text-webpack-plugin");

After making these changes, you config file should look something like this:

var path = require("path"); 
var ExtractTextPlugin = require("extract-text-webpack-plugin");
var DIST_DIR = path.resolve(__dirname, "dist"); 
var SRC_DIR = path.resolve(__dirname, "src"); 

var config = { 
  entry: SRC_DIR + "/app/index.js", 
  output: { 
    path: DIST_DIR + "/app", 
    filename: "bundle.js", 
    publicPath: "/app/" 
  }, 
  module: { 
    loaders: [ 
      { 
        test: /\.js?/, 
        include: SRC_DIR, 
        loader: "babel-loader", 
        query: { 
          presets: ["react", "es2015", "stage-2"] 
        }
      },
      { 
        test: /\.css$/, 
        loaders: ["style-loader", "css-loader", "sass-loader"] 
      },
      { 
        test: /\.less$/, 
        loader: ExtractTextPlugin.extract("css-loader!sass-loader") 
      } 
    ] 
  }, 
  plugins: [ 
    new ExtractTextPlugin("src/components/assets/css/style.css", { 
      allChunks: true 
    }) 
  ] 
}; 

module.exports = config;