.corner {
  z-index: 10;  
}
.corner-absolute {
  position: absolute;
}
.corner-fixed {
  position: fixed;
}

.corner-top-left ,
.corner-top-right {
  top: 0;
}
.corner-bottom-left ,
.corner-bottom-right {
  bottom: 0;
}

.corner-top-left,
.corner-bottom-left {
  left: 0;
}
.corner-top-right,
.corner-bottom-right {
  right: 0;
}