gtk: Make background-color of some components in popover transparent

src/_sass/gtk/_common-3.20.scss

@@ -1631,6 +1631,10 @@ popover.background {

                                
                                
                                
                            
                                
                                    
                                        
                                            1631  
                                                background-color: transparent;
                                        
                                        
                                            
                                            
                                            
                                            
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        
                                            1632  
                                              }
                                        
                                        
                                            
                                            
                                            
                                            
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        
                                            1633  
                                            
                                        
                                        
                                            
                                            
                                            
                                            
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1634 +
                                          list,
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1635 +
                                          .view,
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1636 +
                                          toolbar { background-color: transparent; }
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        1637 +
                                        
                                        
                                        
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        
                                            1638  
                                              // &.touch-selection,
                                        
                                        
                                            
                                            
                                            
                                            
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        
                                            1639  
                                              // &.magnifier,
                                        
                                        
                                            
                                            
                                            
                                            
                                        
                                    
                                
                                
                                
                            
                                
                                    
                                        
                                            1640  
                                              // &.osd { @extend %osd; }