In order to make ScrolllView 's style for "RadHtmlPlaceholder" , you have to use "css". However, this would work only in IE and not other browsers. For a more detailed explanation of this problem, please take a look at the following link: http://iconico.com/CSSScrollbar/
You can also take a look at the attached sample which I prepared for you. Let me know if you have more questions.
the Telerik team