Run this code: http://jsfiddle.net/msz9Lpfe/ ```css #container { transform: scale(1); border: 25px solid; height: 100px; } #fixed { position: fixed; } ``` ```html <div id="container"> <div id="fixed"></div> </div> ``` ```js fixed.append("top: ", getComputedStyle(fixed).top); ``` If the containing block of a fixed positioned element is derived from an ancestor element, then it should be the ancestor's padding area (*). This means that "top: auto" should resolve to "top: 0px", but getComputedStyle says "25px" instead. Note that if you set "top: 0", the element stays at the same position as with "top: auto", and with "top: 25px" it's shifted downwards. So the element is painted at the right position, this is just a getComputedStyle problem. Neither Firefox nor Chromium have this problem. (*) The spec doesn't define that for fixed positioning, but it's how browsers behave and is consistent with absolutely positioning, which is properly defined in the spec.
In fact, all values are currently affected. However, in https://bugs.webkit.org/show_bug.cgi?id=188711 I plan to fix all cases except for 'auto' values.
I am able to reproduce this bug using attached JSFiddle from Comment 0 and it shows "25px" for Safari 15.6.1 and STP 152 while it shows "0px" for Chrome Canary 107 and Firefox Nightly 106. Thanks!
<rdar://problem/99533470>