z-index usage should be documented

Users of Cauldron need to know how to work with the z-index approach of Cauldron

This would allow us to avoid the following (see screenshot) and the CSS hacks that are then required to get around this.


No file, test, or documentation entry point is identified in the issue. Start by locating Cauldron's existing user documentation and the z-index styles or components it describes; done means users can understand the z-index approach and avoid the CSS hacks shown in the screenshot.

Written by the indexing model from the issue text.