The stronger together theme is that boxes are able to go over the void tiles (and the later seen bridge tiles) when at least one box in a chain is on the ground, hence they are stronger together. Another small form of it comes that they are able to weigh down bigger buttons when there are more of them together although that's a slight stretch as many of the buttons are single ones and it's also not coded that way. Thanks for the feedback and I'll make sure to check your game out!
EDIT: I checked out your game and it was a nice experience. Cool mechanic with really nice art!