With this Plone Addon you can add local styles within a subsection of your Plone site.
After installation you can upload a css file, named localstyles.css
anywhere to a folderish content item. This css file is then included for this
folder and all content items below. The traversing stops for ISite based
objects, which a localstyles.css file within a ISite (e.g. a
collective.lineage site) isn't used for folders, which are in higher
hierachy of the content tree.
This product registers a viewlet named collective.localstyles.viewlet,
which is included in plone.app.layout.viewlets.interfaces.IHtmlHead and is
responsible for injecting the localstyles.css file.
This product is inspired by this discussion: http://plone.293351.n2.nabble.com/CSS-for-a-single-page-td7559936.html