Rated 4 out of 5 stars

I love this theme.

My only problem is that I can't really distinguish between a new item in my inbox and the selected ones. It'll be great if you use a different background for the selected emails.

This review is for a previous version of the add-on (9.0.4). 

If I didn't do it, it s because it was creating problems with the background color for tagged e-mails (which needs to have a specific color). And til now I didn't find better solution than how it is actually (i.e. unread e-mail has a bold blue font which is different than selected one who is simply blue).
By the way, I don't know if you are aware of it, but in the messages list header there is a little icon on the right side which allows you to select which columns to display or not. When you click on it, it opens a dropdown menu, then simply check if the "read" (I think it s like this in english, my TB is in french so I don't know the exact translation for english TB version) option is enabled or not, If its not enabled, enable it and then it will add a small column in the mail list and it will show an orange dot beside unread mails. Like this you ll have a very explicit way to distinguish new items from selected one.