How can I change the css on a sub site

I am working with a CherryFramework theme and I have installed it on Multi site. I loaded the framework and then the theme for it. Once I went into the theme and changed the css, my subsites are still having the same css as previous to the change. Also when I de activate and re-activate it reverts back to the old css. Part of the framework uses less.php and I am sensing that there is a cahse problem of some sort. ANy thoughts would be appreciated. Thank you