Why is it impossible to change content in css?

Question

CSS2.1 pseudo-selectors such as ::after and ::before allows to add text content to the page. For example :

CSS

Answer 1

The CSS 2.1 spec cited says: “Applies to: :before and :after pseudo-elements”. This restriction has been relaxed in the draft for CSS3 Generated and Replaced Content Module, which is old (2003) and outdated but still partly implemented. Opera seems to support content for normal elements, except for the use of URL values (used to insert images), whereas Chrome and Safari do the same only for URL values. So you code actually works on Safari.

More widespread support is not very likely unless specification work on the module makes some progress. On the W3C CSS module status page, the module is in the “Rewriting” section, with the note “Severely outdated”.