Why are date selection component's select inputs not themed ?

The select inputs inside the date picker look native and do not seem to follow the theme.

It can be seen easily on that page : http://demo.vaadin.com/sampler/#DateResolution
The select for the resolution has the theme applied to it, if you change the resolution to “minute” for instance, the selects which are added in the date component have the default browser style applied to them.

Is there a way to have them nicely themed too ? (if possible without the need to copy/paste the css for selects)