Add this at the bottom of your file:

   # Version 2.4:
   # %value% Current page
   # %value1% Pages count
   cosmeticsSelector_nextPage:
      mat: "@eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvMTE3ZjM2NjZkM2NlZGZhZTU3Nzc4Yzc4MjMwZDQ4MGM3MTlmZDVmNjVmZmEyYWQzMjU1Mzg1ZTQzM2I4NmUifX19@"
      title: "&9Next page"
      slot: 50
   cosmeticsSelector_prevPage:
      mat: "@eyJ0ZXh0dXJlcyI6eyJTS0lOIjp7InVybCI6Imh0dHA6Ly90ZXh0dXJlcy5taW5lY3JhZnQubmV0L3RleHR1cmUvNWFlNzg0NTFiZjI2Y2Y0OWZkNWY1NGNkOGYyYjM3Y2QyNWM5MmU1Y2E3NjI5OGIzNjM0Y2I1NDFlOWFkODkifX19@"
      title: "&9Previous page"
      slot: 48