Working with the WordPress Editor
The WordPress Editor lets us edit the files that power our theme. It's accessible from the WordPress dashboard and easy to use. But, it's important to remember that, unlike posts and pages, WordPress does not track revisions to these files. You should always back up your theme files before changing them in the Editor.
So, once we've made a backup (which I prefer to do using FTP), we can open up the Editor and work on our stylesheet.