Board Thread:Support Requests - Getting Technical/@comment-46854292-20200916151510/@comment-9605025-20200916163326

Anything outside the article content is considered a "standard Fandom feature" because it all contributes to the uniform layout across all wikis. "Outside the article" includes the right rail and the page header (where the page title and edit buttons are). There is precedence for Fandom to allow style changes and insertion of additional modules into the right rail. However, removal of right rail modules and changes to anything else outside the article content is prohibited unless otherwise stated. An example of "otherwise stated" would be changing the local navigation via ThemeDesigner and MediaWiki:Wiki-navigation. The penalty for violating the customization policy depends on the offense and the discretion of the staff member dealing with the offense.

All that said, I don't think the CSS CrazyForMyself proposed will work on UCP wikis. Is your wiki a UCP wiki or a legacy wiki?