How do I make unread notifications more noticeable?

I’ve been editing a lot of the CSS of my forum, but I can’t for the life of me figure out what to target in order to change the appearance of new/unread notifications. You can see in the picture below that by default there’s barely any difference between new notifications and old ones:

I’m wanting to add a light blue background behind unread notifications to make them more noticeable, but I’m not able to isolate just unread notifications. I’ve only been successful at changing the look of ALL notifications, not just unread ones.

Anyone know what I’m supposed to type?

Try the following:

.user-menu .quick-access-panel {
  background-color: red;
  .read {
     background-color: var(--secondary);