Themeing mechanism for custom elements

It would be nice to have a themeing mechanism baked into the browsers for
custom elements, pages, and the whole app.  Most UI Widget frameworks today
have themeing built in, such as Jquery UI, KendoUI, Wijmo, ect ect. Oses and
some other non-web applications have themeing, heck even our browsers can
have custom themes.  I know the Polymer team is working on making a solution
for Polymer by creating custom, re-usable, sharable themes, but this is on a
framework by framework basis.  

 

I would like to see a spec for themes either for css as a whole or
web-components.  Another source of inspiration is Asp.net themeing, you can
theme a whole app, individual pages, partial pages, or individual
components.  A standard mechanism would be very useful now that we have
custom elements as a standard, almost :), but themes should not just be
limited to custom elements they should appy to our existing built in ones as
well, buttons, selects, ect.

 

Thanks,

Dan