solid-csd class is not implemented

Per https://gitlab.gnome.org/GNOME/gtk/blob/master/gtk/gtkwindow.c

> * Style classes that are typically used with the main CSS node are .csd (when
> * client-side decorations are in use), .solid-csd (for client-side decorations
> * without invisible borders), .ssd (used by mutter when rendering server-side
> * decorations)

Currently, elementary stylesheet doesn't implement that which causes a large amount of issues. It might be the reason why issuses like the ones with PlayOnLinux, Wine happen on elementary too.