Handling the CSS for effective results

While Handling the CSS we require the changes to take effect  and NO OVERRIDE should take place.
For the moment when we change the CSS values in
1. Style-Orange.CSS.

2. Then we clear the cache.

3.Desired result is seen.

4. After few hours all changes applied to style-orange.css are reverted and NOVERIDE takes place.

Please explain how we should manage this scenario and what step are we missing !!