.contents{
  position: relative;
  height: 300px;
}

.diamond {
  position: absolute;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  width: 200px;
  height: 200px;
  background   : linear-gradient(to bottom, #99ccff, #0059b3);
  transform    : rotate(90deg);
  margin: auto;
}