I noticed that the implementation of z-index has varying values with a 1070 spread:

I was wondering what the rationale is behind this implementation of z-index. There seems to be groups of content, single digit (2-15) and thousand digit (990-1070).

I ask because 1) y'all are the some of the smartest minds when it comes to css and 2) I am trying to implement some organization in my app's CSS files using this method but it won't work with how bootstrap handles CSS.

Thanks for any insight you can provide.