Step 1:
I layed a white 30x30 cm paper on a pink one and folded the box out of this combined paper.
Prefold in half over the two centerlines, they're already made in this photo.
Then fold the upper and lower half in three parts of the same size.

Step 6:
Fold the corner upwards, use the prefolded lines as guidance.

Step 5:
Fold over this prefolded line.

Step 2:
Fold both parts in half and unfold the model afterwards.

Step 4:
Cut the white paper into this size, use the prefolded squares pattern as guidance.

Step 3:
Repeat step 1 and 2 in this direction.

Step 10:
Squash-fold the flaps around the corners.

Step 8:
Repeat step 6 and 7 on the other three corners.

Step 9:
Fold the four flaps against the model, use tape or glue.

Step 7:
Make sharper folding lines.

Step 16:
Prefold over these four lines.

Step 15:
This is the other side.
Fold the eight mountain-fold-lines about 1/4 (prefolded) square sidewards.

Step 12:
I layed a white 15x15 cm paper on a purple paper for the lid.
Fold in three parts of the same size and then in half. Unfold and repeat in the other direction.

Step 11:
Done....

Step 14:
Make sharper prefolded lines.

Step 13:
Fold the upper and lower edge to the prefolded line.

Step 19:
Fold the edges straight downwards, use tape or glue on the corners.

Step 18:
Prefold over these four lines.

Step 17:
Fold all corner edges into a straight line.