Bsrgvty

I would like to change the background color of the pop out menu of the Top Bar in the lockscreen and unlockscreen of Ubuntu 18.04 (using GDM). It appears when I clicked the "power, sound, network" button located at the far right end of the top bar. I would like to know the name of the css selector to make this change. I tried this change but nothing happened.

/* Popovers/Menus */
.popup-menu 
 min-width: 15em; 
 .popup-menu .popup-sub-menu 
 background-color: yellow; /* changed from #3a3a34 to yellow */
 box-shadow: inset 0 -1px 0px #2c2c28; 
 .popup-menu .popup-menu-content 
 padding: 1em 0em; 
 .popup-menu .popup-menu-item 
 spacing: 12px; 
 .popup-menu .popup-menu-item:ltr 
 padding: .4em 1.75em .4em 0em; 
 .popup-menu .popup-menu-item:rtl 
 padding: .4em 0em .4em 1.75em; 
 .popup-menu .popup-menu-item:checked 
 background-color: #3a3a34;
 box-shadow: inset 0 1px 0px #2c2c28;
 font-weight: bold; 
 .popup-menu .popup-menu-item.selected 
 background-color: rgba(238, 238, 236, 0.1);
 color: #eeeeec; 
 .popup-menu .popup-menu-item:active 
 background-color: #dd4814;
 color: #ffffff; 
 .popup-menu .popup-menu-item:insensitive 
 color: rgba(238, 238, 236, 0.5); 
 .popup-menu .popup-inactive-menu-item 
 color: #eeeeec; 
 .popup-menu .popup-inactive-menu-item:insensitive 
 color: rgba(238, 238, 236, 0.5); 
 .popup-menu.panel-menu 
 -boxpointer-gap: 4px;
 margin-bottom: 1.75em; 

What is the correct way of doing what I want?

from the standard ubuntu.css file the below part is what you are looking for. Concentrate on "green" color.

.popup-menu-boxpointer,
.candidate-popup-boxpointer 
 -arrow-border-radius: 3px;
 -arrow-background-color: green;
 -arrow-border-width: 1px;
 -arrow-border-color: #1f1f1c;
 -arrow-base: 24px;
 -arrow-rise: 11px;
 -arrow-box-shadow: 0 1px 3px black; 

Edit: Concentrate on Blue & Yellow colors in below.. Hope you can manage further..

/* Popovers/Menus */
.popup-menu 
color: blue;
 min-width: 15em; 
 .popup-menu .popup-sub-menu 
 background-color: blue;
 box-shadow: inset 0 -1px 0px #2c2c28; 
 .popup-menu .popup-menu-content 
 padding: 1em 0em; 
 .popup-menu .popup-menu-item 
 spacing: 12px; 
 .popup-menu .popup-menu-item:ltr 
 padding: .4em 1.75em .4em 0em; 
 .popup-menu .popup-menu-item:rtl 
 padding: .4em 0em .4em 1.75em; 
 .popup-menu .popup-menu-item:checked 
 background-color: #3a3a34;
 box-shadow: inset 0 1px 0px #2c2c28;
 font-weight: bold; 
 .popup-menu .popup-menu-item.selected 
 background-color: rgba(238, 238, 236, 0.1);
 color: yellow;