buildbot.css and default.css were used by old buildbot (v0.8) (http://docs.buildbot.net/0.8.5/manual/cfg-statustargets.html). Since we have updated to new buildbot version on build.webkit.org (See Bug 175056), these files are unused and can be deleted.
Created attachment 426946 [details] Patch
Comment on attachment 426946 [details] Patch rs=me
buildbot.css was added in http://trac.webkit.org/changeset/15099/webkit ~15 years back!
Committed r276540 (236984@main): <https://commits.webkit.org/236984@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 426946 [details].
<rdar://problem/77093414>