Get classes on DOM elements that are untracked by C++ and managed by Bootstrap

[lemniscate8]

I've written added a toggle handler on the Card class which fires when a card is opened or closed. However, this would be more powerful if the hander's signature included a boolean indicating the Card's state at time of click so that different events could take place on open or close.
Unfortunately, the Card's state is entirely managed by CSS and Javascript from Bootstrap. Thus, it would be useful if there existed a method on Widget or Div to read in any classes or state we don't manage/track in C++. I imagine this would also have other applications eventually.