WebKit: Table cells containing vertical or sideways `writing-mode` child ignores line height, renders at incorrect width

[querkmachine]

Upstream bug: https://bugs.webkit.org/show_bug.cgi?id=313826
Date: 2026-05-01
Reported by: @querkmachine
Related to: N/A

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Overview

When a table cell contains a child element that has a writing-mode of either vertical-* or sideways-*, the line height (and/or block-axis dimension) of that element's content is ignored when computing the width of the table cell. This results in the content being visually rendered outside of the table cell.

This does not occur if the writing-mode is set on the table cell itself, only for child elements. It also does not occur if the value of writing-mode is one of the horizontal-* values. Margins, padding and borders all contribute to the width calculation as expected, with only the content height being disregarded.

Reproduction: https://codepen.io/querkmachine/pen/ByQyYrW

Expected result

As rendered in Chrome 147 and Firefox 150.

Actual result

As rendered in Safari 26.4.