Support negative pixels in CSS engine
Currently using negative pixel values, for example for absolute positioning, in the GNOME Shell CSS files causes several artifacts (e.g. duplicate mouse cursors, flickering...) and (potentially dangerous?) unexpected behaviours to appear. To avoid these issues:
- either support for negative dimensioms should be added (but do we really need it?)
- or any dimension below 0 should be ignored (and thus set to 0) where unsupported, possibly with some kind of CSS linter or runtime warning
The issue was verified on 3.34, not sure if this behaviour was solved since