By default, publishing an NPM package sets the "latest" tag to the version in that package, regardless of whether there exists a newer (in the sense of higher) version for that package already. In practice, this means that publishing @webref/css@v6 after @webref/css@v7 effectively make v6 the latest version that gets installed when running npm install @webref/css.
The publishing logic should handle that and make sure the publication of a former version does not update the "latest" tag. I believe that's doable by passing another tag name as part of the publication. If that does not work, updating the latest tag afterwards with npm dist-tag add @webref/css@x.y.z latest (with the right latest version) would work.