Port 6ab9e10efa to v3

https://webkit.org/b/147284 has been fixed
Refs #16814
[ci skip]

docs/_data/browser-bugs.yml

@@ -198,16 +198,6 @@
   origin: >
     Bootstrap#16372
 
--
-  browser: >
-    Safari
-  summary: >
-    Incorrect placement of `position: fixed` element when it's a child of a `position: relative; left: X%;` element.
-  upstream_bug: >
-    WebKit#147284, Safari#21993128
-  origin: >
-    Bootstrap#16814
-
 -
   browser: >
     Safari (OS X)