Various embodiments enable particular CSS pseudo-classes to be employed, but limit particular functionality aspects of those pseudo-classes that can lead to divulging personally identifiable information. Thus, various embodiments can change how a CSS pseudo-class is allowed to function. For example, in at least some embodiments, CSS pseudo-classes are permitted to be used to make the visual formatting changes to a web page, but not structural formatting changes. That is, changes that do not affect the structure of content within a web document are allowed, while changes that affect the structure of the content are not allowed.