Phi/add mini css

[Pailowmenah]

When ran locally, I am seeing

[webpack-cli] Failed to load '/home/phi/repositories/simple-keyboard/webpack.config.js' config
[webpack-cli] Error: Cannot find module 'mini-css-extract-plugin'

I ran npm install mini-css-extract-plugin and now the issue is resolved.

Testing

• Verified that the package can now be installed via npm install @bearrobotics/simple-keyboard@3.8.9 without failure.
• Verified that core-ui can be built properly when pointing to the test version

[github-actions]

👋 Hello @Pailowmenah! Please make sure to review the Contributing Guidelines to ensure your PR is compliant. Thank you!