No color highlighting because of missing CSS properties

[florianbuehler]

Description

The code highlighting of the VS Code stylelint extension and other projects depend on the CSS properties listed in grammar/css.cson.

Due to missing CSS properties, the highlighting is currently not working for accent-color, ascent-override, descent-override, line-gap-override and size-adjust.

To fix this the properties need to be added to grammar/css.cson.

[Tirjasdyn]

As of now, no syntax highlighting is working on CSS