Local CSS in the UofL plone 4 system is easier to use and more flexible than before. There is no need to upload a file and hope it works any more. You can also allow the local CSS from the parent folder to be inherited by the child folder so there is less repetition.
When you edit a page (web page, form, blog...) or folder there will be two extra fields. The first one is a text box in which you can enter your CSS for the page or folder. The second one is a check box "Block CSS Inheritance" when not checked the page or folder will inherit it's parent Local CSS settings. This means that if you have a local CSS on a folder any page that is in that folder will also have those CSS changes. If you want one page to be different check the box and the folder's CSS will not show up.