Hello, I think it’s because the Do not disturb and Log Out are buttons, not links. That is why only the buttons color change because it won’t override the links color. I think If you want to change all menu item color you have to target both links and buttons.
I think here you target the wrong class there is a more specific one for tabs. For example here you can target the tab id. #quick-access-notifications.
Something like this…
#quick-access-notifications {
&.quick-access-panel li a {
color: red;
}
}