That will set the time limit for caching, but you still can't force the browser to request a new version when you change the contents of the stylesheet. This doesn't matter so much for trivial changes, but if you make major changes you're still going to want to either rename the file or use ?something to effectively rename the file. That way on the the next page request the browser gets the updated version and everything renders correctly. Otherwise there may be layout issues until the cached copy expires.