CSS is not optimized for graphics and if you're only interested in something static, in this case for instance the result is bigger than an equivalent PNG file. It also sucks for client-side optimizations in general because rendering CSS takes more processing power than displaying a bitmap.

What it does give you is smooth animations, however I think SVG would be more suited for vector graphics, since it is a format created and optimized for actual graphics and you can export from popular editors (like from Adobe Illustrator) to SVG easily.

Not to belittle this effort though, as this is cool :)