Apply theme CSS to only one UI widget (or remove css per widget)

Apply theme CSS to only one UI widget (or remove css per widget)


I'm using the datepicker and the tabs and I'd like to use the
lightness theme for the datepicker, but my own custom CSS (not the
lightness theme CSS) for the tabs.
Maybe an api option to not apply the theme-specific classes to an
individual widget would be a good feature to add - or am I missing
something?
Thank you!