docs: add off-canvas scrollbox
docs: add off-canvas scrollbox

abdullahsalem/foundation-sites,zurb/foundation-sites,DaSchTour/foundation-sites,zurb/foundation,zurb/foundation-sites,abdullahsalem/foundation-sites,zurb/foundation,zurb/foundation-sites,DaSchTour/foundation-sites,zurb/foundation,abdullahsalem/foundation-sites