Rated 5 out of 5 stars

I've just been trying this out even though I don't mind the standard icons. I do like the look and colour of these ones, though. Just one little issue. For my Gmail account folders, the theme doesn't recognise the "Bin" folder (UK Gmail) as a wastebin and therefore that is just assigned a standard folder icon. Other accounts with a "Deleted" folder get the correct icon. No big deal, but it would be nice to see the waste icon associated with the Bin folder.

Just confirmed. By changing my Gmail account temporarily to language English (US) , when the deleted folder is now called "Trash" and Thunderbird labels it "Deleted" , the proper wastebin icon is assifned. Change it back to English (UK) and it goes back to a standard file folder.

Thank you, Dillinger, that seems to work. Cheers for getting back to me so rapidly.

This review is for a previous version of the add-on (3.0b5). 

Confirmed, but I don't think this is an add-on issue, apparently Thunderbird 78 does not pick the new "Deleted" folder automatically after changing the Gmail language.

After changing the language, go to Server Settings of your Gmail account and adjust "When I delete a message" manually.