Cool js app[0]! I often have to look up flexbox properties. After level 4 of this game, align and justify are definitely more clear in my mind now. It also helps to see over and over in each level that these properties are for the flex parent.

Edit: later levels (~10) begin to help with the discerning the difference between the flexbox main and cross axes.

[0] https://github.com/thomaspark/flexboxfroggy/