What you can do, is utilize the Div function like this.
<div style="height: 200px; width: 300; overflow: auto ">txt; banner, etc</div>
The overflow: auto is usable if you want to have a srollbar.
You don't need to have an external sytle sheet. Its primary purpose is to have your web settings cached with the browser, which overtime will speed up the loading speed of your web pages.
Hope this helps