see https://searchfox.org/wubkat/search?q=horiztonalBorder&redirect=false
<rdar://problem/116164873>
Pull request: https://github.com/WebKit/WebKit/pull/18331
Committed 268574@main (99d5287148f2): <https://commits.webkit.org/268574@main> Reviewed commits have been landed. Closing PR #18331 and removing active labels.