Inquiry: How to style the first child of a group?

[emms-gh]

Hello folks!

I was looking through the default style.css found in /ext/xdg/waybar and saw that we can change the style of the first child of the modules by doing something like

.modules-left > widget:first-child > #workspaces { margin-left: 0; }
so I have tried to do it in my group, however, I am unable to do changes on the first child of a group when all of it's content is shown. I have tried these codes

.modules > widget:first-child > #custom-power {background-color: red;} #session > widget:first-child > #custom-power { background-color: red; } #session > #custom-power {background-color: red;} .modules-right > #session > .modules > widget:first-child > #custom-power{ background-color: red;}
and my group config looks like this

"group/session": { "orientation": "inherit", "tooltip": false, "drawer": { "transition-duration": 500, "children-class": "not-power","transition-left-to-right": false}, "modules": ["custom/power","custom/lock","custom/reboot"] }
What I am trying to achieve is that when I hover on group/session and once all child is revealed, I want the #custom-power to have a different background than the rest.

I am hoping to hear from you folks, and thank you for taking time to answer this.