The sonar-css-plugin you linked is not maintained by SonarSource. SonarSource has, however, created their own CSS analyzer plugin (which Tibor is referencing). It appears that your IT department installed SonarSource’s CSS analyzer rather than the one you linked. The github repo for the “official” SonarCSS analyzer is located here: https://github.com/SonarSource/sonar-css
Having used the sonar-css-plugin that you linked: it’s pretty noisy and not updated very often. Updates also don’t appear in the marketplace as the maintainer has, so far as I understand it, left the SonarQube community.
I would reccomend going with SonarSource’s CSS plugin, since it’s more “official” and you are guaranteed some level of support through forums like this for false-positives, reccomending new rules, etc.