In the article Swing and CSS, Joshua Marinacci shows a simple implementation of a CSS-like system for styling Swing interfaces. It’s an interesting idea, and the implementation looks potentially flexible enough to do interesting things. However, I agree with some of the commenters that what this is trying to do is essentially the same as what L&Fs are all about. Maybe the syntax will be more accessible to non-programmers.
CSS is great for the web, because the web is presenting documents. Swing is not used for presenting documents… it’s used for creating desktop applications, which (generally) should have a consistent L&F with the rest of the desktop. If you’re making MP3 playing software, sure, you may want to make that skinnable. But, for large business applications you want something that looks like a normal desktop app. Standard Swing L&Fs are designed to do that (regardless of how well they succeed at that task).