CSS Changes, Updates in ASP.NET Theme Does Not Show Up

I thought it may be cached, but f开发者_StackOverflow中文版or some reason that I don't know the changes I make in CSS file that is located in application theme does not show up. If I take that change and put in a CSS file outside of theme folder, let's root or a new folder, it does show up. This is a ASP.NET 4.0 application. Not sure where to look for the solution. Please advise.

Don't just put the Theme folder, create a sub folder and put under it. It is better to name both sub-folder and css file same.