Responsive Foundation 6.0.0

A base z-index to use for overlays and lightboxes. This z-index will always be on top unless you are using $z-index-dev. Use this variable alone to set a default z-index which will play nicely with other types of interactive content on your site. Use + or - with it to set a z-index relative to the default overlay. Change this variable to change the stacking order of all overlays. (You may want to do this if you have a fixed sticky navigation so that the sticky navigation isn't always on top, even with lightboxes.)