The pattern-library is installed as a npm-package in the Platform Client. For development, it is not suitable to publish a package for each change, and luckily, there is hack you can do to test the styles locally instead.
Make sure the Pattern-library is built through running gulp build in the terminal
Copy all contents in the "assets" folder
Go to your Platform-client folder
Navigate to node_modules/ushahidi-platform-pattern-library folder
Remove the contents in the "assets" folder
Paste the contents you copied from the assets-folder in the pattern-library
Done! Now you should be able to see the changes in the Platform Client
Further reading
After setup, please read the Platform Pattern Library guidelines when working with the Platform Pattern Library.