Get the position of a fixed div with jquery

.offset() gives you the coordinates relative to the whole document.

The .offset() method allows us to retrieve the current position of an element relative to the document. Contrast this with .position(), which retrieves the current position relative to the offset parent. When positioning a new element on top of an existing one for global manipulation (in particular, for implementing drag-and-drop), .offset() is the more useful.

.offset() returns an object containing the properties top and left.

Note: jQuery does not support getting the offset coordinates of hidden elements or accounting for borders, margins, or padding set on the body element.

you can use .offset() to get the current coordinates of the element relative to the document whereas .position() to get the current coordinates of an element relative to its offset parent.