From time to time I see an experienced wikian write that your personal monaco.css (Special:MyPage/monaco.css) will only affect a site's skin if the Monaco Custom skin has been selected by the site's admin.

  • This is fiction.

Regardless of whether a site's admin has specified:

  1. Default
  2. Monaco Custom
  3. Monaco Slate
  4. ... or any of the other preset Monaco skins

a user's personal monaco.css will layer on top of (i.e. take precedence over) any Monaco skin style at that wiki.

This has been verified using both non-sysop and sysop user accounts at a pristine test wiki.