Create z-index system

[ChrisBrettCA]

z-indexing can often be a minefield causing most devs a headache and resulting in something like:

z-index: 10000;

to force a component to sit above all else.
Let's be mindful of this and create a system that stages components at different levels perhaps.

[ChrisBrettCA]

Aeroplane ceiling heights... ?

[btomy]

https://css-tricks.com/handling-z-index/ - this seems like a good idea with sass map