I'm surprised that an article that says "stackable" in the first sentence doesn't have a picture to show the chairs stacked together.
Two examples:
https://payload.cargocollective.com/1/12/412300/6034129/stac...
https://i.pinimg.com/736x/27/cb/7c/27cb7c5a2e9610cff78e47ce5...
Hopefully someone has (or can take) a freely licensed image to add to the article.