This time around, I really only have one suggestion for taking the concepts in this chapter further.
Create your own Zen Garden design! It doesn't have to be the most beautiful design ever, nor does it have to be submitted, although you're certainly encouraged to do so if you like. All you need to do is create one or more style sheets that present the Zen Garden base file in a new and interesting way. Try different layouts with the markup, making them more and more complex as you learn. Remember: The markup is not to be touched. All you can do is write CSS. When you hit a limitation, see if you can find a creative way around it. Try things that don't seem like they have a chance in Hades of working. When you make a mistake, stop before you undo it. Was the result interesting in a way you didn't expect? If so, try following that path instead of the one you meant to follow. You never know what interesting technique or effect you might find just by working in the Zen Garden.