Using your favorite text or code editor, create a file in that folder called macworld.css. Once the file’s in place, switch back to Safari and the Extension Builder window.

If you find yourself doing repetitive tasks in your browser, it may be time to try writing an extension for Chrome or Firefox—with just minimal coding knowledge required.

Note: When you create a new Chrome extension, you normally need to provide several types of files, depending on how complex it is.

Learn how to create folders by file extensions on Windows 11/10. You can sort files by extensions or formats using this guide.