gtk-3.24.26 CSS change can trigger a crash in mutter for tiled SSD windows
The code in mutter that uses gtk to draw server side decorations assumes that the overall size of the decoration does not change between the focused and unfocused state. This got broken with 56f6ac5f which introduced a 20px invisible shadow for the unfocused state of SSD windows when they are tiled, because
.tiled:backdrop is more specific than
.ssd. Now whenever a user clicks somewhere in the 20px region below the titlebar, this will confuse mutter and lead to a crash (more details about the mutter side can be found here: mutter#1668 (comment 1046828)).