Depending on the browser, it might be a caching problem.
There may be a setting in your browser that is preventing the Cache from updating.
Have you tried to reset your browser to defaults?
The reason I ask, is Firefox and Chrome handle this way differently.
If you clear the cache+cookies in Firefox, it might not take effect until you close ALL Browser windows.
Chrome will refresh the cache with each individual tab.
I would suggest maybe re-installing your browser because this definitely appears to be a local issue, but not affiliated with the css itself.
