Once you have assembled the seat base and the seat cushion, line the back edges up with each other and glue the cushion to the top of the seat base. Leave to dry.
Apply a small amount of glue to the side edges of the seat base and the cushion. Cut out the seat sides and slip the square sections just under the top of the seat cushion and into one of the fold as the bottom of the seat base, lining up the rounded edges so they match the seat base and the seat cushion. Run a bone folder or the edge of a fingernail along the faint line between the seat cushion and seat base on the side cover, to make a tiny step between the two sections (see photo). Press the side section into the glue on the sides, trim the front edge of the side if necessary to make it fit your chair seat.
Repeat for the other side.
