You sorta can use CSS, but they are hard properties in Java. You're better off using a LookAndFeel manager instead. Customizing the actual L&F is quite a bit of work in Java; its not simple like CSS and HTML is (but that's all HTML/CSS' job is, so I think that's a fair trade).
You can see some screenshots and download links for a few themes here: http://geeknizer.com/best-java-swing...casual-top-10/
Scrolling in Java gui is very simple. Simply add the scrollable content to a JScrollPane and add that panel to the frame instead of the large component. Without customizing a thing, the JScrollPane's job is to determine the viewport size you have and add scrollable content to it.