Theming and Installing Local Grunt

I am having issues installing local grunt in my plone theme. My OS is Ubuntu 16.04 and I have the following installed:
$ node --version
$ npm --version
$ grunt --version
grunt-cli v1.2.0

I have also done the following:
$ sudo cd src/plonetheme.shared
$ sudo npm install grunt --save-dev
$ sudo cd src/plonetheme.shared/src/plonetheme/shared/theme
$ sudo npm install bootstrap --save

However, when I run
zeocluster/src/plonetheme.shared/src/plonetheme/shared/theme$ sudo grunt

Loading "Gruntfile.js" tasks...ERROR
>> Error: Cannot find module 'autoprefixer'
Warning: Task "default" not found. Use --force to continue.

Aborted due to warnings.

Am I missing something? Any advise would be most appreciated.

Are you following instructions in our docs or training? (if so, which ones?)

For the record, here is how I go through this issue:
$ npm install autoprefixer --save-dev

And you might also need these:
$ npm install grunt-browser-sync --save-dev
$ npm install grunt-contrib-watch --save-dev
$ npm install grunt-contrib-less --save-dev
$ npm install grunt-postcss --save-dev

Thanks so much. It is much appreciated!