Black borders around client-side decorated windows when toggling compositing
KDE bug report: https://bugs.kde.org/show_bug.cgi?id=440235
When compositing is turned off, client-side decorated GTK applications have black border around them where the client-side drop shadow used to be. This is reproducible with Breeze GTK and other GTK themes. For example, https://bugsfiles.kde.org/attachment.cgi?id=140308
Note that the application won't have a black border around it if it's launched while compositing is off. It seems like GTK doesn't add .solid-csd
CSS style class when compositing is toggled, it does so only on startup.