292516 2025-05-04 21:09:41 -0700 Inserting a subgrid child with `position: absolute` can cause `auto` column widths to be calculated incorrectly. 2025-05-11 21:10:12 -0700 1 1 1 Unclassified WebKit Layout and Rendering Safari 18 Mac (Apple Silicon) macOS 14 NEW InRadar P2 Normal --- 1 dwarn webkit-unassigned bfulgham karlcow sgill26 simon.fraser webkit-bug-importer zalan oldest_to_newest 2114995 0 dwarn 2025-05-04 21:09:41 -0700 Overview: Inserting a subgrid child with `position: absolute` can cause `auto` column widths to be calculated incorrectly. --- Reproduction: 1. Go to https://codesandbox.io/p/sandbox/sleepy-noyce-vynd7s 2. Hover over the subgrid element to inject an element. 3. Or click the 'toggle inserted element' button. --- Generic Steps to Reproduce: 1. Create a grid with an `auto` width column and at least one other non-`auto` width column. 2. Create a subgrid that spans the entire parent grid. 3. Have a child that is always visible as part of the subgrid in the `auto` column. 4. Insert an absolutely positioned child in the non-`auto` column, after the initial load. 5. (Optional) remove the second child, the bug remains. --- Actual Results: The `auto` width column has an incorrect width. It looks like it is being treated as `1fr` instead. --- Expected Results: The `auto` width column should not be affected by the addition of a sibling with `position: absolute`. The initial column width, before inserting the absolutely positioned second child, is correct and consistent with other browsers. --- Build Date & Hardware: Safari 18.3 (19620.2.4.111.8, 19620) on MacOS 14.7.2 --- Additional Builds and Platforms: Not reproducible on Chrome or Firefox. 2116026 1 karlcow 2025-05-08 19:36:41 -0700 This is interesting because sometimes I get the right layout. After a while the dashed border around subgrid child is exhibiting the right width. it takes a couple of seconds. 2116405 2 webkit-bug-importer 2025-05-11 21:10:12 -0700 <rdar://problem/151125072>