Lustra and French Curve solid plastic toilet seats have thin plastic covers over the bolts that attach to the toilet seats. They are designed to close with a pin and socket design and cover the head of the bolt.
If your cover snaps open and won't close, use a needle nose pliers to gently crimp the two pins; attempt to close the cover and reopen it (Fig. 1). If you are satisfied with results, close the cover. If not, attempt the re-crimp technique again.