Remember this book? Gnomes by Wil Huygen, illustrated by Rien Poortvliet (1977).
My parents have a set of little plastic book-shaped Christmas light covers with Poortvliet's gnome illustrations on them. It's not a huge set, just enough for a short string, but it went up on our Christmas tree every year.
I'm a bit disappointed that my web-searching hasn't yielded an image to share because these light covers are so charming. Just thinking about them makes me happy as I'm reminded of tree-trimming and holiday preparations.