There is at least one toolkit around that can do this: Qt. Yes, you can only use it from C++ in a meaningful way, but it has all the building blocks for designi

There is at least one toolkit around that can do this: Qt. Yes, you can only use it from C++ in a meaningful way, but it has all the building blocks for designing, styling and animating UIs that you might wish for. I don't think the extent to which this is possible is known by most HN users. It is quite easy to write e.g. conditional widget style sheets that change widget appearance based on widget state (e.g. failing input validation) without a single line of C++ code required. WPF can also be styled extensively, at least in theory, but this is much harder to accomplish. MS has developed Blend to assist with this, but you still need a deep knowledge of the internal hierarchy if elements of a widget to get good results.