I like Clojure and design at an enthusiastic amateur level but I don't know CSS. I want to set up a project to get fast feedback as I learn it and develop some ideas. I know that I'll be trying out different typefaces, working with grids, experimenting. I'd like to not have to refresh anything manually. Is this a job for figwheel, shadow-cljs, something else?

Both figwheel and shadow-cljs are suitable. I'd recommend you start with https://github.com/day8/re-frame-template and the +garden option to experiment with css