Use kdoctools' kde-docs.css instead of kio_docfilter.css
kio_docfilter.css got out of sync with with kdoctools, e.g. for the header. Using the same CSS as the application manuals also results in visual consistency across documentation presentations.
Still using kdoctools5, not 6, given right now I am unsure which Qt version will be used with distributions with konqueror (asking in sysadmin/repo-metadata!283 (comment 915007)).
See similar work for man (network/kio-extras!346 (merged)) & info (network/kio-extras!347 (merged))
After:
Before:
