Highlight of collapsed thread with unread message in Thunderbird

The default highlighting mechanism for collapsed threads that contain an unread message is to underline it. However, I found that this visual clue is not enough

The below code in userChrome.css can make the collapsed threads with unread message both highlighted and in read color

/* change unread thread color */
treechildren::-moz-tree-cell-text(container, closed, hasUnread, read)
{
color: red !important;
}