The spec says this property shouldn't be inherited, and it doesn't seem to be needed anymore after decorating-box based painting. This was my testcase: data:text/html,<p style="text-decoration-thickness: 20px; text-decoration-line: underline; text-decoration-color: black"><span>hello</span></p>
Pull request: https://github.com/WebKit/WebKit/pull/3871
Committed 254010@main (002f683d6859): <https://commits.webkit.org/254010@main> Reviewed commits have been landed. Closing PR #3871 and removing active labels.
<rdar://problem/99406505>