As an alternative, I decorated the white side of the paper with some drawings, as shown in the picture below.
I used two 6" x 12" (150 mm x 300 mm) rectangles of scrapbook paper, one for the bottom and another for the lid. According to the instructions, the folding sequence starts by dividing the paper into 5ths, both for the base and for the lid. For the base I followed the instructions, dividing the paper into 5 equal parts (2.4 inches each), but for the lid I folded one 2" section and then divided the rest in four equal sections of 2.5" instead (the 2" section is the one that goes inside when forming the box).
With this proportions the sides of the lid are a little longer than the sides of the bottom and the lid fits nicely on it.