Prettier for CSS files

A stack of patches recently landed that enable Prettier for formatting CSS files in the main Firefox repo. This brings formatting for CSS more in line with how we already format JS, HTML, and other front-end languages.

You should now be able to format CSS files using ./mach lint -l stylelint or ./mach format. I would also recommend configuring your editor/IDE of choice to enable Prettier to format CSS files on save, if possible. If you use VSCode you can run ./mach ide vscode to set this up.

I plan to expand Prettier formatting to SCSS files in the near future.

If you have any questions or concerns don't hesitate to reach out via the #lint:mozilla.org channel on Matrix.

Cheers,

Hanna