Determine appropriate z-index value via JS

[Schepp]

A z-index value of 999 should cover a lot of cases but is still not the ideal value to apply. Z-Index should be determined via JS if available.

[drublic]

What would be a good way to do it? This might mean that we would have to parse the whole CSS and find the highest z-index.
Also if this happens automatically you cannot layer anything above the actual modal. This might be needed on smaller screens when building an app-like website.
Apart from that it is possible to set the z-index in the SCSS file as a variable.