Right now creat-react-app supports SASS by default. So to add less support we need to eject first and then edit “webpack.config.js” file. To eject configuration run following command:

npm run eject

And install less loader and less

npm install -S less less-loader

Now search following:

const sassRegex = /\.(scss|sass)$/;
const sassModuleRegex = /\.module\.(scss|sass)$/;

And replace with

const sassRegex = /\.(less)$/;
const sassModuleRegex = /\.module\.(less)$/;

Now we need to replace SASS loader with less loader. Find the following lines:

{
              test: sassRegex,
              exclude: sassModuleRegex,
              use: getStyleLoaders(
                {
                  importLoaders: 2,
                  sourceMap: isEnvProduction && shouldUseSourceMap,
                },
                'sass-loader'
              ),
              // Don't consider CSS imports dead code even if the
              // containing package claims to have no side effects.
              // Remove this when webpack adds a warning or an error for this.
              // See https://github.com/webpack/webpack/issues/6571
              sideEffects: true,
            },
            // Adds support for CSS Modules, but using SASS
            // using the extension .module.scss or .module.sass
            {
              test: sassModuleRegex,
              use: getStyleLoaders(
                {
                  importLoaders: 2,
                  sourceMap: isEnvProduction && shouldUseSourceMap,
                  modules: true,
                  getLocalIdent: getCSSModuleLocalIdent,
                },
                'sass-loader'
              ),
            },

in the above lines replace text “sass-loader” with “less-loader”. Now the part of your file which has above code will look like:

{
              test: sassRegex,
              exclude: sassModuleRegex,
              use: getStyleLoaders(
                {
                  importLoaders: 2,
                  sourceMap: isEnvProduction && shouldUseSourceMap,
                },
                'less-loader'
              ),
              // Don't consider CSS imports dead code even if the
              // containing package claims to have no side effects.
              // Remove this when webpack adds a warning or an error for this.
              // See https://github.com/webpack/webpack/issues/6571
              sideEffects: true,
            },
            // Adds support for CSS Modules, but using SASS
            // using the extension .module.scss or .module.sass
            {
              test: sassModuleRegex,
              use: getStyleLoaders(
                {
                  importLoaders: 2,
                  sourceMap: isEnvProduction && shouldUseSourceMap,
                  modules: true,
                  getLocalIdent: getCSSModuleLocalIdent,
                },
                'less-loader'
              ),
            },

And that’s it. You can now write LESS.