[rlander]

Unless you accidentally close or reload the browser window (or there's a power failure). This has happened to me more times than I care to remember.

[BasDirks]

I create a "task" (you can do this with any todo app, but I use taskwarrior) for every change I make to my css, ie: "more appropriate top margin @ index". Then I solve exactly that problem, change the selectors/properties I need in my stylesheet, and review the solution (to see if other rules are affected or overwritten).

define problem -> solve problem -> refine solution -> commit/save changes.

might sounds slow, but really isn't, and keeps things clean.