It seems conceivable that one could use CSS to style the SVG-rendered charts similar to how we style the HTML of Table (and other HTML-rendered charts). The style role is even formatted similar to CSS, but the similarity is somewhat of an illusion since it could not be used directly in the SVG.
But I like the idea of extending our CSS-like notation to support classes. We'd probably want a way of representing the CSS in JSON, so it could be specified in the options object. Is there a library we could leverage that does that already?