Add a full screen "Open in tab" button

[Carreau]

The button appear next to the "Go back" button once a user has already shown the iframe.

[martinRenou]

Thanks! Would you be able to add it to the jupyterlite-sphinx docs so we can test it here?

[Carreau]

yeah, this is just a draft I submitted before going to lunch, i should have marked it as such. i'll do that later, as well as document and tweak the css.

[Carreau]

It works on RTD:

and is also affected by custom CSS:

[martinRenou]

Really nice thanks!