How to calculate the slope of a square in three dimensions

Question

Suppose I have a square which has the following coordinates at its corners:

A (0, 0, 10); B (0, 10, 7); C (10, 10, 8); D (10, 0, 5)

Drawn with GeoGebra, it looks something like this:

Is it possible to calculate a "total" slope of the square in reference to the x-y plane, e. g. it has a slope of 30° and if yes, how to do it?

(Some ressources would also be greatly appreciated)

Answer 1

This isn't a square because, for example, the distance AB is not the same as BC.

Also, the points are not in n the same plane, so talking about the slope is not meaningful.