Chrome DevTools - Live Edit CSS, Save to Disk
Here's how it works: (1) make changes to styles as you do (2) you can click through to the Sources pane and live-edit styles there, just like a text editor. (3) Right click and save to disk. choose where to save the file (4) Make some more changes (5) Just hit ctrl-s (or cmd-s) to immediately save back to disk in the same location.