Flyout: scroll the menu when there is too many versions

[humitos]

Related: readthedocs/readthedocs.org#7375

[zanderle]

Do we also want to make the header of the flyout sticky, so that it is always shown, even when we scroll down?

[humitos]

Do we also want to make the header of the flyout sticky, so that it is always shown, even when we scroll down?

Yes. That would be great 👍🏼

[zanderle]

Do we also want to make the header of the flyout sticky, so that it is always shown, even when we scroll down?

Yes. That would be great 👍🏼

Oops, that PR (#126) didn't include this yet. Do you want me to reopen this or create a separate issue?