Bearing in mind that all browsers (in common use) that support border-radius and gradients, also support SVG and canvas, and that SVG and canvas let you do more, are generally more performant, and have fallbacks (SVG particularly) in older browsers, why would you use Donatello?
I have to admit, I was also slightly irritated when I actually checked out the repo. The title is deceptive. "Donatello, a JS drawing library" - which is what it is - would probably not rack up as many points. Interesting tool, I hope to check it out sometime, but the OP should have been a little more honest. Just call it what it is.
The title inside the main file is a little more honest: "A pure CSS vector drawing library" meaning that the vectors created are CSS only (not Canvas).
This whole ninja turtles thing is going to get out of hand. I already know of at least one other Donatello library based on Raphael.js which does something different.
Thanks i'm aware of my Renaissance art, but the things that connected Donatello the artist to Raphael the artist is being italian and a gap of nearly 20 years, in the reverse order you would think, given that there are now two derivative libraries built on Raphael named Donatello.
The ninja turtles connection is, even if you were talking about the artists, the more likely link :P