For WordPress plugin developers, the metabox API generally proves to be invaluable. Meta boxes allow you to organize various bits of information, groups of options and more into nice, attractive, collapsible boxes rather easily. What’s more, these boxes can be dragged around the screen and reorganized without much hassle. However, one thing that you can’t do with meta boxes is to assign additional CSS classes to them.
However, in WordPress 3.2, you will be able to do just that. WordPress 3.2 will introduce a brand new filter that allows you to modify the list of classes that are applied to a meta box. In order to use it, you’ll need to know the slug of the page on which the meta box is being displayed and the ID of the meta box.