You need an 11 x 11 piece of designer paper. Lie the side you want to see on the table and fold into a triangle. On the folded edge, measure and score upwards at 3" and 5 1/2". Measure down from the tip and score across at 3 1/2". Cut away the small triangles that are formed by thes core lines. Open the corners at the fold and press to create diamonds.
The left one can be taped down and sealed. The right side can be taped down but do not seal as this is where the top slips in to close the card. Decorate as you desire. I hope this makes sense. Let me know if you have any questions and good luck.