Fold your strap in half lengthwise and sew down the long edge. Right side out, iron and then cut in half. Tuck one end of each piece in and then sew closed.
Take your main pocket pieces (mine were 13X16) with right sides together then sandwich the straps between the pocket pieces.
Sew around leaving a hole. Flip the pocket right side out.
Iron and then sew the hole closed.
Fold the pocket on itself however deep you want the pocket then sew along the edge (just right on top) and down the middle to form the pockets.
Sew the buttonholes and if you’re making covered buttons make those (tute here). Sew buttons on the strap.
All you have to do left is to attach it to your chair and fill the pockets on the Ikea STIG that I used you can just pop off the seat and loop the straps around the frame.