Full on-the-fly stylesheet editing in Chrome or Safari
Thanks to you I found it!
The Live Stylesheets extension for Chrome is what you are looking for. Be sure to restart Chrome after installation to use it.
You can edit external stylesheets in Chrome DevTools, too (since Chrome 15 or so). Just double-click the stylesheet contents in the Resources panel (or click the "Edit" button below), edit, Ctrl-S to commit a new revision, Esc to cancel editing. And it updates your page as you type!
You can edit your CSS files directly on Chrome without relying on any extension.
Here is how: Edit CSS files on the fly using Chrome DevTools
A different way to access it: