I just made one this past week, and listed the pattern on Ravelry. It's in Japanese, but here are the basics:
You chain 19 (18 across and 1 for the first sc), and sc 18 back and forth for 20 rows. On the odd rows (except row 1), increase the first sc and decrease the last sc. On the even rows, decrease the first sc and increase the last sc. Don't forget to ch 1 at the beginning of each row.
This particular pattern uses 2 colors, but I used one color in an ombre colorway. If you want the 2 color stripes, change color at the end of each even row. The pattern also instructs you to sc in the back loop only, so you get nice little ribs.
After the 20th row you slip stitch the top and bottom together. Finally, you run your yarn through each side and draw it in the center tightly. You can make a hanging loop with a ch 12 (I left this part off on mine).
The pdf pattern link is next to the diagram graphic (below the button graphic).