1. Take out A4 paper (other larger paper is also acceptable) and fold the paper in half once along the long side.

2, and then along the long side of this time, it becomes a thin strip.

3. Cut the paper into thin strips and take two pieces.

4. Glue one end of two paper tapes together.

5. Paint the whole side of the post-it note with color (green or black).

6. Twist one end of the note 180 degrees, that is, turn it over, and then stick this section with the other end of the note to form a Mobius ring.