editing style.css in my admin panel don't change any in my site

in my website in admin panel even i change like example the color font-size padding in my admin panel style.css it change but when i reload my site, don’t change anything, but when i double check i see the changes and when i view source the css have a version. I edit style.css but when i view sour it come `style.css?ver=3.5.1′ is that my theme problem or what somebody can explane why