Reactjs - Demo Application is not working

rm -rf node_modules
npm cache clean --force
npm install

now try again to run your scripts, it should work

https://github.com/react-toolbox/react-toolbox-example/issues/28

I'm able to solve the problem. The problem is that package-lock.json is pointing to the older packages.
To fix, uninstall an install the package again

Uninstall package

$ sudo npm remove csstools/normalize.css

After that, we have to install again

$ npm install csstools/normalize.css

(removing sudo from the npm install command)