It's not really feasible. Rich clients in Java are done using Swing or SWT.
If you want to use HTML/CSS for your user interface, you need to use the server/client model. It can be as simple as creating a local server and launching a browser that connects to it, but it would still be that model.
If you absolutely need to have HTML/CSS as your UI framework and can't go to a server/client model, your best bet is probably looking at something like Google Native Client, but that uses C/C++ bindings on the backend. I haven't used Native Client so I can't personally give much more information on that front.
Edit to add:
One option is to embed a native browser into your Swing app using something like: http://djproject.sourceforge.net/ns/
There are some pure Java HTML renderers, however, they most likely won't be fully HTML5/CSS3 compliant, let alone possibly have Javascript bugs as well.
See here for some of those options: Pure Java HTML viewer/renderer for use in a Scrollable pane