.land_prev {
 width: 25%;
 height: 100%;
 position: fixed;
 left: 0;
 top: 0;
 z-index: 12;
}

.land_next {
 width: 25%;
 height: 100%;
 position: fixed;
 right: 0;
 top: 0;
 z-index: 12;
}