What does the * * CSS selector do?

Question

Recently I came across * * in CSS.

Site reference - Site Link.

For a single * usage in CSS style sheet, Internet and Stack Overflow is flooded with examples, but I am not sure about using two * * symbol in CSS.

I googled it, but unable to find any relevant information about this, as a single * selects all elements, but I am not sure why the site used it twice. What is the missing part for this, and why is this hack used (if it is a hack)?

Answer 1

Just like any other time you put two selectors one after another (for example li a), you get the descendant combinator. So * * is any element that is a descendant of any other element — in other words, any element that isn't the root element of the whole document.