css/* More specific selector */
.slds-dropdown.comm-user-profile-menu__dropdown-ctn {
    background-color: rgb(75, 155, 101, 1) !important;
}

/* Even more specific */
.comm-user-profile-menu__dropdown-ctn.slds-dropdown.slds-dropdown_right {
    background-color: rgb(75, 155, 101, 1) !important;
}

/* Target with all classes */
.comm-user-profile-menu__dropdown-ctn.slds-dropdown.slds-dropdown_right.slds-nubbin_top-right {
    background-color: rgb(75, 155, 101, 1) !important;
}
.slds-dropdown__list a.menu-item,
.slds-dropdown__list a.menu-item:hover,
.slds-dropdown__list a.menu-item:focus,
.slds-dropdown__list a.menu-item:active {
  color: #ffffff !important; /* keep text white */
}

.slds-dropdown__list a.menu-item:hover,
.slds-dropdown__list a.menu-item:focus {
  background-color: #0176d3; /* Salesforce brand blue */
}