Hippo Canvas
The Hippo Canvas is a Cairo/GObject/GTK+ based canvas, written in C with support for flexible layout, CSS styling, and initial work on animations.
Code
Currently maintained in GNOME's git: http://git.gnome.org/cgit/hippo-canvas/
Bindings
Bindings for Python are included in the source tree.
Examples
See the tests/ directory in the source.
Documentation
A page on HippoCanvas/CSS.