For grid containers specifically, margin-trim discards the corresponding margin of each grid item in the grid track adjacent to the relevant box edge. This process ignores any collapsed grid tracks. It does not otherwise ignore any empty grid tracks. https://w3c.github.io/csswg-drafts/css-box-4/#margin-trim-grid
<rdar://problem/103285873>
Pull request: https://github.com/WebKit/WebKit/pull/8220
Committed 258587@main (e8f3117677da): <https://commits.webkit.org/258587@main> Reviewed commits have been landed. Closing PR #8220 and removing active labels.