.layer{
   position: relative;
   margin: 0 auto;
}
.buntop{
   z-index: 6;
}
.veggies{
   z-index: 5;
}
.cheese{
   z-index: 4;
}
.meat{
   z-index: 3;
}
.lettuce{
   z-index: 2;
}
.bunbottom{
   z-index: 1;
}