gtk: Drop the background of nested headerbars

src/_sass/gtk/_common-3.20.scss

@@ -1289,6 +1289,16 @@ headerbar {

                                
                                
                                
                            
                                
                                    
                                        
                                            1289  
                                                margin-top: 5px;
                                        
                                        
                                            
                                            
                                            
                                            
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        
                                            1290  
                                                margin-bottom: 5px;
                                        
                                        
                                            
                                            
                                            
                                            
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        
                                            1291  
                                              }
                                        
                                        
                                            
                                            
                                            
                                            
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1292 +
                                        
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1293 +
                                          &.titlebar headerbar:not(.titlebar) {
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1294 +
                                            // Drop the background of non-titlebar nested headerbars. This is needed to
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1295 +
                                            // work around headerbar sliding animation issues without refactoring
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1296 +
                                            // Adwaita's support of titlebars and headerbars as it may break
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1297 +
                                            // applications.
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1298 +
                                            // See https://gitlab.gnome.org/GNOME/gtk/issues/1264 for more information.
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1299 +
                                            background-color: transparent;
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1300 +
                                            box-shadow: none;
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1301 +
                                          }
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        
                                            1302  
                                            }
                                        
                                        
                                            
                                            
                                            
                                            
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        
                                            1303  
                                            
                                        
                                        
                                            
                                            
                                            
                                            
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        
                                            1304  
                                            .background .titlebar {