Possibility to add css class on .v-contexthelp-bubble level

Hi

   There is no easy way to add css class to .v-contexthelp-bubble. Problem for example with windows. If I want to show selected context help only on specific windows. For now z-index of .v-contexthelp-bubble is lower than vaadin window. But in this situation I can't show context help on vaadin window.

Could You take a look on it?

Regards
