Textbox sidebars - responsive resizing and oEmbed

Many apologies if this is something that is already under discussion and development (or if this is simple user error!), but I was wondering if it would be possible to alter the way that textbox sidebars behave on narrow windows and mobile devices. It would be nice for the sidebar to transform into a screen-width element in these contexts:

This text uses the McLuhan theme.

PS: I also wanted to say thank you. The textbox sidebars are a fantastic addition.

Brief addendum:

I noticed, too, that while oEmbeds render as videos within the sidebar textboxes, the videos tend to extend outside of the frames.