[crandles]

If its just a matter of styling, then there is a movement to make styling these sort of components as accessible as anything else on the web. Its still in spec, but you should take a look at the Shadow DOM.

Not the most familiar with it, but I believe the gist of it is to allow developers to create self-contained widgets (or at least part of its usefulness). With it, you'll also be able to access/manipulate browser elements (they'll be presented with a Shadow DOM interface just like a custom widget).

Think styling an HTML5 Video/Audio Player. Each browser may have their own interface, but they'll be built using components, and you'll have access to them using CSS/Javascript in your web page. With the Shadow DOM, you should be able to manipulate said datepicker.

edit: styling a video tag example http://blog.romanliutikov.com/coding/discover-the-dark-side-...