Customizing the appearance is one place where Swing's age shows. It is possible to create a custom "Look and Feel", but it is not as easy as HTML / CSS:
I remember >10 years ago there used to be some "plaf" libraries that provided very easy themeing abilities for Swing that even came with a WYSIWYG tool to create themes. It is a shame something like that never became part of Swing itself and instead you have to create tons of classes just for a theme.
