Gul is a Xul-like / easy glade-like XML markup language for describing user interfaces with PHP-GTK extension. Gul simplifies writing client-side GUI applications. CSS is partially supported.
Gul 2.0 is a powerfull and free Xul parser/interpreter library for Phpgtk 2 written in php. Gul supports PHP and basic CSS features into Xul. Gulpad example provides a split screen where the Xul code can be typed and immediately previewed.