Bug 242313 – margin-bottom wraps into next column if columns are of uneven height

• Status: NEW
• Component: Layout and Rendering

[Kimberly Grey]

Created attachment 460652 [details]
HTML example (duplicate of Codepen)

## Steps to reproduce

1. Open the Codepen at https://codepen.io/querkmachine/pen/ExEVVBL or the attached HTML file in Safari. 
2. Ensure the viewport is wide enough for the content to be presented in two columns without text wrapping.

## Expected behaviour

List items 1 to 7 appear in the first column, list items 8 to 13 appear in the second column. 

The tops of both columns are vertically aligned with one another. 

## Actual behaviour 

List items 1 to 7 appear in the first column, list items 8 to 13 appear in the second column.

The top of the second column appears 20 pixels below the top of the first column, as the `margin-bottom` from list item 7 is being rendered above list item 8. 

In this example, the issue is triggered by a combination of an odd number of list items and the last list item having the bottom margin reset to 0, creating a large enough difference in column lengths for the margin to wrap.

I could also reproduce this in the Safari 16 beta. The columns appear as expected in Firefox and Chromium browsers. 

## Potentially related bugs

- https://bugs.webkit.org/show_bug.cgi?id=17887
- https://bugs.webkit.org/show_bug.cgi?id=105411 
- https://bugs.webkit.org/show_bug.cgi?id=212505

[Kimberly Grey]

Created attachment 460653 [details]
Screenshot of issue in Safari 15.5

[Radar WebKit Bug Importer]

<rdar://problem/96815456>

[Karl Dubost]

Usually adding an outline on elements has no influence on the layout as they do not participate to the computation of width and so on. 

But I forked the codepen of Kimberley and added outline for the list items.

and surprise, "it made it work"
https://codepen.io/webcompat/pen/rNdMBvK

As a note, do not use the technique to align the items, because this would have consequences for accessibility.

[zalan]

Created attachment 460810 [details]
Test reduction

It looks like our multicol code gets confused when collapsing margins across columns.

[Ahmad Saleem]

(In reply to zalan from comment #4)
> Created attachment 460810 [details]
> Test reduction
> 
> It looks like our multicol code gets confused when collapsing margins across
> columns.

Something similar to this?

https://chromium.googlesource.com/chromium/src.git/+/506506eac78a8106c4e92866a59b8c724ddc8b88

[Derk-Jan Hartman]

Isn't this another case of 104944 ?