How to find the column position of an element? Or how to find an element by column position?

In a Web page, I have a list (ul) of elements (li). Thanks to CSS columns, the elements are spread in several columns.

I want to know:

1. In what column is a given element?
2. Is a given element the first one, or the last one, in its column?
3. What is the first element, or the last element, in a given column?

How can I do that? In JavaScript, for example. Maybe in CSS selectors?

Thank you.