Hi @YuzaTea, thanks for taking the time to report this and welcome to Wikimedia Phabricator! In the future, please always follow https://www.mediawiki.org/wiki/How_to_report_a_bug
This needs to be fixed in https://ko.wikipedia.org/wiki/미디어위키:Vector.css . On-wiki content like user scripts, gadgets, templates, custom CSS are local features and managed independently on each wiki.
Phabricator is mostly used for MediaWiki, MediaWiki extensions, or server configuration, or by developers and teams to organize what they plan to work on. Phabricator is not a place to ask for help with your own local code.
This needs fixing on the local wiki. Hence I am closing this task here.
If you are looking for help with your own code, see https://meta.wikimedia.org/wiki/Small_wiki_toolkits#Ask_your_technical_questions instead - thanks for your understanding!
See "Future changes" on https://meta.wikimedia.org/wiki/Tech/News/2020/25 and on https://meta.wikimedia.org/wiki/Tech/News/2020/21 for more information about recent changes in the Vector skin, and links how to fix problems.