can’t change scrollbars

Hi everybody, I’m french, so please excuse my very bad english. I want to change the scrollbars, but when I do it on wp-layout, it doesn’t change anything in my browser. I’ve put my blog into an iframe on my page, and the scrollbars are the typical ones, grey. I’ve tried so many things to change that, that I don’t know what else I could do. I don’t know if it will help but here is my blog adress : http://ylang-nae.net/indexblog.html
I would really appreciate a little help because I don’t know what to do now…Thanks a lot !!