The phrase "to decorate the box" means to make the outside of something look more attractive or interesting without really changing what's inside.
Sentences with «to decorate the box»
Rather than putting gifts in boxes and then wrapping them, why not just put them in the box and decorate the box with non-toxic paint or stamps? (wellnessmama.com)
I've overlooked decorated boxes in the past but this table changed my mind. (aroundmytable.com)