CSS: position:fixed inside of position: fixed

Question

Okay, I\'ve noticed something, but couldn\'t find it in the CSS spec. Styling an element with position: fixed will position it absolutely, with respect to the b

Answer 1

This only occurs when one of the ancestors of an element that uses position: fixed has defined (with a value different that none) any of the following styling rules: filter, transform, perspective, where, in this case, the closest ancestor that matches this condition will be used as the reference for the coordinates of the element instead of the viewport.

From MDN

fixed

The element is removed from the normal document flow, and no space is created for the element in the page layout. It is positioned relative to the initial containing block established by the viewport, except when one of its ancestors has a transform, perspective, or filter property set to something other than none (see the CSS Transforms Spec), in which case that ancestor behaves as the containing block. (Note that there are browser inconsistencies with perspective and filter contributing to containing block formation.) Its final position is determined by the values of top, right, bottom, and left.

This value always creates a new stacking context. In printed documents, the element is placed in the same position on every page.